Combinatorial discovery of nanomaterials

ABSTRACT

Methods for discover of ceramic nanomaterial suitable for an application by preparing an array of first layer of electrodes and printing ceramic nanomaterial films on the electrodes. A second layer of electrodes is printed on the nanomaterial films of ceramics to form an electroded film array. The electroded film array is sintered. Properties of the sintered electroded film array are measured and one of the array elements with properties suited for the particular application is identified.

RELATED APPLICATION

The present application is a continuation of copending U.S. patentapplication Ser. No. 10/811,628 filed on Mar. 29, 2004 entitled“NANOMATERIAL COMPOSITIONS WITH DISTINCTIVE SHAPE AND MORPHOLOGY” whichis a continuation of U.S. patent application Ser. No. 10/449,278 filedon May 20, 2003 entitled “INORGANIC COLORS AND RELATED TECHNOLOGY” whichis a division of U.S. patent application Ser. No. 10/150,722 filed onMay 17, 2002 entitled “NANOTECHNOLOGY FOR INKS AND DOPANTS” is adivisional of U.S. patent application Ser. No. 09/274,517 filed on Mar.23, 1999 entitled “MATERIALS AND PRODUCTS USING NANOSTRUCTUREDNON-STOICHIOMETRIC SUBSTANCES” now U.S. Pat. No. 6,344,271 which claimsthe benefit of provisional application No. 60/107,318, filed Nov. 6,1998, entitled “MATERIALS AND PRODUCTS USING NANOSTRUCTUREDNON-STOICHIOMETRIC MATERIALS,” and which claims the benefit ofprovisional application No. 60/111,442 filed Dec. 8, 1998 all of whichare assigned to the assignee of the present invention and which areincorporated herein by reference.

The present application is also a continuation-in-part of co-pendingU.S. patent application Ser. No. 09/790,036 titled “NANOTECHNOLOGY FORDRUG DELIVERY, CONTRAST AGENTS AND BIOMEDICAL IMPLANTS” filed on Feb.20, 2001 which is a divisional of U.S. Pat. No. 6,228,904 filed on May22, 1998, which is incorporated herein by reference and which claims thebenefit of U.S. Provisional applications 60/049,077 filed on Jun. 9,1997, 60/069,936 filed on Dec. 17, 1997, and 60/079,225 filed on Mar.24, 1998. U.S. Pat. No. 6,228,904 is a continuation-in-part of U.S.patent application Ser. No. 08/739,257, filed Oct. 30, 1996, now U.S.Pat. No. 5,905,000, titled NANOSTRUCTURED ION CONDUCTING SOLIDELECTROLYTES, which is a continuation-in-part of U.S. Ser. No.08/730,661, filed Oct. 11, 1996, now U.S. Pat. No. 5,952,040 titled“PASSIVE ELECTRONIC COMPONENTS FROM NANO-PRECISION ENGINEERED MATERIAL”which is a continuation-in-part of U.S. Ser. No. 08/706,819, filed Sep.3, 1996, now U.S. Pat. No. 5,851,507 titled “INTEGRATED THERMAL PROCESSFOR THE CONTINUOUS SYNTHESIS OF NANOSCALE POWDERS” and U.S. Ser. No.08/707,341, filed Sep. 3, 1996, now U.S. Pat. No. 5,788,738 titled“METHOD OF PRODUCING NANOSCALE POWDERS BY QUENCHING OF VAPORS”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to combinatorial discovery of stoichiometric andnon-stoichiometric substances and more particularly to nanostructuredsubstances and products incorporating such substances.

2. Relevant Background

Most compounds are prepared as stoichiometric compositions, and numerousmethods of preparing substances for commercial use are motivated inobjective to create stoichiometric compounds. For example, producers oftitania fillers, copper oxide catalysts, titanate dielectrics, ferritemagnetics, carbide tooling products, tin oxide sensors, zinc sulfidephosphors, and gallium nitride electronics all seek stoichiometriccompositions (TiO₂, CuO, BaTiO₃, NiFe₂O₄, TiC, SnO₂, ZnS, and GaN,respectively).

Those skilled in the art will note that conventional powders of oxidesand other compounds, when exposed to reducing atmospheres (e.g.hydrogen, forming gas, ammonia, and others) over a period of time, aretransformed to non-stoichiometric materials. However, the time and costof doing this is very high because the inherent diffusion coefficientsand gas-solid transport phenomena are slow. This has made it difficultand uneconomical to prepare and commercially apply stablenon-stoichiometric forms of materials to useful applications.

Limited benefits of non-stoichiometric materials have been taught byothers; for example, Sukovich and Hutcheson in U.S. Pat. No. 5,798,198teach a non-stoichiometric ferrite carrier. Similarly, Menu in U.S. Pat.No. 5,750,188 teaches a method of forming a thin film ofnon-stoichiometric luminescent zinc oxide. The film is a result of athermodynamically favored defect structure involving non-stoichiometriccompositions where the non-stoichiometric deviation is in parts permillion.

A very wide variety of pure phase materials such as polymers are nowreadily available at low cost. However, low cost pure phase materialsare somewhat limited in the achievable ranges of a number of properties,including, for example, electrical conductivity, magnetic permeability,dielectric constant, and thermal conductivity. In order to circumventthese limitations, it has become common to form composites, in which amatrix is blended with a filler material with desirable properties.Examples of these types of composites include the carbon black andferrite mixed polymers that are used in toners, tires, electricaldevices, and magnetic tapes.

The number of suitable filler materials for composites is large, butstill limited. In particular, difficulties in fabrication of suchcomposites often arise due to issues of interface stability between thefiller and the matrix, and because of the difficulty of orienting andhomogenizing filler material in the matrix. Some desirable properties ofthe matrix (e.g., rheology) may also be lost when certain fillers areadded, particularly at the high loads required by many applications. Theavailability of new filler materials, particularly materials with novelproperties, would significantly expand the scope of manufacturablecomposites of this type.

SUMMARY OF THE INVENTION

This invention includes several methods of making non-stoichiometricsubmicron and nanostructured materials and devices from bothstoichiometric and non-stoichiometric precursors. This invention alsoincludes methods of making stoichiometric materials and devices fromnon-stoichiometric precursors. In one aspect, the invention includes animproved sintering technique utilizing submicron non-stoichiometricpowders. The invention also includes a variety of other applications forsubmicron non-stoichiometric materials, including catalysis, photonicdevices, electrical devices and components, magnetic materials anddevices, sensors, biomedical devices, electrochemical products, andenergy and ion conductors.

In one aspect, this invention includes a variety of methods of producinga non-stoichiometric material. According to one method, a submicronpowder of a stoichiometric material is transformed into anon-stoichiometric powder. The submicron powder may also be ananopowder. If desired, the submicron non-stoichiometric powder may besintered into a bulk substance.

According to another method, a non-stoichiometric submicron material isproduced by quenching a high-temperature vapor of a precursor materialto produce a non-stoichiometric submicron powder. A vapor stream of thehigh temperature vapor flows from an inlet zone, and this stream ispassed through a convergent means to channel the vapor stream through anarea where flow is restricted by controlling the cross-section of theflowing stream. The vapor stream is channeled out of the flowrestriction through a divergent means to an outlet pressure which issmaller than the inlet pressure. This quenches the vapor stream. Theinlet and outlet pressures are maintained, creating a pressuredifferential between them. The pressure differential and thecross-section of the flow restriction are adapted to produce asupersonic flow of the vapor stream. This method may further comprisesintering the resulting powder.

According to yet another method, a nanoscale starting materialcomprising more than one element is provided. At least one of theseelements is an electropositive element. A dopant element with valencydifferent than the electropositive element is added, and the mixture isheated to a selected temperature, preferably greater than the solidstate reaction temperature, for a time sufficient to allow interminglingof the dopant element and the given electropositive element.

According to still another method, two nanopowders are mixed in a ratioselected to produce a desired non-stoichiometric composition. The firstnanopowder comprises a plurality of materials, and the second comprisesa subset of those materials. The materials comprising the firstnanopowder may be metallic, semimetallic, non-metallic, or anycombination thereof. The mixture is heated in a selected atmosphere to atemperature to produce a solid state reaction. The atmosphere mayparticipate in the solid state reaction. This invention also includesthe materials produced via the above methods.

In another aspect, this invention includes a submicronnon-stoichiometric material where the value for a selected physicalproperty of the submicron non-stoichiometric material is greater than10% different from that for a stoichiometric form of the submicronnon-stoichiometric material. Alternately, the relative ratios of thecomponents of the material differ by more than 1% from thestoichiometric values, preferably 2% from the stoichiometric values, andmore preferably 5%. The material may be a nanomaterial or a nanopowder.

This invention also includes a submicron material wherein a domain sizeof the material is less than 500 nm, and the material isnon-stoichiometric. Preferably, the domain size is less than 100 nm.Alternately, a domain size may be less than 5 times the mean free pathof electrons in the given material, or the mean domain size may be lessthan or equal to a domain size below which the substance exhibits 10% ormore change in at least one property when the domain size is changed bya factor of 2. The material may be a powder or a nanopowder.

In another aspect, this invention includes a method of determining thenon-stoichiometry of a material. A stoichiometric form of the materialand the material whose stoichiometry is to be ascertained (the “unknown”material) are heated separately in a reactive atmosphere to 0.5 timesthe melting point of the material. The weight change per unit sampleweight for the unknown material is monitored. In addition, the weightchange per unit sample weight of the unknown material is compared to theweight change per unit sample weight of the known material.

In another aspect, this invention includes a method of conductingcombinatorial discovery of materials where non-stoichiometric forms ofmaterials are used as precursors.

In another aspect, this invention includes a method of making anon-stoichiometric nanoscale device by fashioning a non-stoichiometricnanoscale material into a device. Alternately, a device is fashionedfrom a stoichiometric material and the stoichiometric material convertedinto a non-stoichiometric form. The stoichiometric material may be anelectrochemical material, a photonic material, or a magnetic material.The non-stoichiometric material may be electroded; and the electrode maycomprise a non-stoichiometric material. This invention also includesstoichiometric devices with non-stoichiometric electrodes. Thenon-stoichiometric materials may further be nanomaterials.

In another aspect, this invention includes a method of producing astoichiometric material from a non-stoichiometric powder. The powder isprocessed into the shape desired for a stoichiometric material andfurther processed to produce stoichiometric ratios among its components.This invention also includes a method of producing a stoichiometricdevice via the same method.

In another aspect, this invention also includes an improved method ofproducing sintered materials. A submicron stoichiometric powder isformed into a green body. The green body is sintered at a selecteddensification rate and a selected temperature which are lower than thoserequired to sinter larger, stoichiometric powders. This method mayfurther comprise converting the sintered material to a stoichiometricform or stabilizing the non-stoichiometric sintered material by theaddition of a protective coating, secondary phase, or stabilizer. Inthis method, the submicron non-stoichiometric powder may also benanopowders.

This invention also includes a method of producing an improved catalyst.A nanopowder comprising indium tin oxide and alumina are pressed intopellets. The pellets are reduced in a reducing atmosphere to form acatalyst which can promote the formation of hydrogen from 12% methanolvapor at 250° C. This invention also includes the improved catalystprepared by this method.

In another aspect, this invention includes a method of producing animproved photonic material. A high-temperature vapor of a precursormaterial is quenched from a gas stream comprising hydrogen and argon toproduce a non-stoichiometric submicron powder such that the absorptionof selected wavelengths is more than doubled with respect to that of astoichiometric from of the precursor. In this method, the precursormaterial may be stoichiometric ITO; the selected wavelengths would begreater than 500 nm. In addition, this invention includes an improvednon-stoichiometric photonic material produced by this process andexhibiting enhanced absorption of selected wavelengths ofelectromagnetic radiation in comparison to a stoichiometric form of thematerial.

In another aspect, this invention includes a method of producing animproved electric device. Titanium oxide nanopowders are heated in anammonia atmosphere to produce a non-stoichiometric oxynitride oftitanium. The resulting device may also be part of an electricalconductor. This invention also includes the improved electrical deviceproduced by this method.

This invention also includes a variety of methods of making improvedmagnetic materials and devices. According to one method, a nickel zincferrite material is sintered to near theoretical density and heated in areducing atmosphere at an elevated temperature such that the resultingmaterial exhibits higher magnetic loss than the stoichiometric startingmaterial. The atmosphere may comprise 5% H-95% Ar and the temperaturemay be 800° C.

According to another method, a mixture of two stoichiometric nanopowdersis produced from manganese ferrite and nickel zinc ferrite powders.These two powders are pressed together, sintered, and wound. The methodmay further comprise pressing the two nanopowders with a binder,preferably 5% Duramax. This invention also includes the magnetic devicesand materials produced by these methods.

In another aspect, this invention includes methods of making anon-stoichiometric resistor. In one method, the resistor is producedfrom a stoichiometric submicron material and transformed to anon-stoichiometric form. In another method, the resistor is producedfrom non-stoichiometric SiC_(x) nanopowders. The nanopowders aresonicated in polyvinyl alcohol and screened printed on a aluminasubstrate. The resulting resistor element is to produce a resistorhaving a resistance less than 1 megaohm. Platinum or silver dopants maybe added to the sonicated mixture. This invention also includes theimproved resistors produced via these methods and arrays of resistorsproduced via these methods.

In another aspect, this invention also includes a method of producing animproved sensor device. A non-stoichiometric nanopowder is sonicated ina solvent to form a slurry. The slurry is brushed onto screen-printedelectrodes and allowed to dry at to remove the solvent. A dissolvedpolymer may also be included in the slurry. The screen-printedelectrodes may be gold electrodes on an alumina substrate. The screenmay be made from stainless steel mesh at least 8×10 inches in size, witha mesh count of 400, a wire diameter of 0.0007 inches, a bias of 45°,and a polymeric emulsion of 0.0002 inches.

In another aspect, this invention includes an improved sensor deviceprepared from a screen printable paste. A nanopowder and polymer aremechanically mixed; a screen-printing vehicle is added to the mixtureand further mechanically mixed. The mixture is milled and screen-printedonto prepared electrodes. The paste is allowed to level and dry. Thisinvention also includes the improved sensor devices produced by theabove processes.

This invention, in a further aspect, includes a method of making animproved biomedical orthopedic device. A feed powder comprising anon-stoichiometric Ti—Ta—Nb—Zr alloy is milled under non-oxidizingconditions. The milled powder is mixed with a binder dissolved in asolvent and allowed to dry. The mixture is then pressed and incorporatedinto a biomedical device. This invention also includes a biomedicalmaterial comprising a non-stoichiometric submicron powder. In addition,this invention includes a biomedical material produced by this processwherein the powder is a nanopowder.

This invention, in another aspect, includes a method of preparing animproved electronic component. A non-stoichiometric nanoscale materialis mixed with a screen printing material and the resulting pastescreen-painted on an alumina substrate. The paste is wrapped up anddried on a heated plate and further screen-printed with silver-palladiumto form a conducting electrode. The silver-palladium is dried rapidly ona heated plate and the two films co-fired.

In another aspect, this invention includes an improved electrochemicalmaterial comprising a submicron non-stoichiometric material. Thematerial has excess Gibbs free energy in comparison to larger grainedmaterials. In addition, the material exhibits increased solutediffusion, lower phase transformation temperatures, and high compressivetoughness.

In another aspect, this invention includes a method of making animproved energy and ion conducting device. A stoichiometric nanoscalestarting powder is reduced at a temperature between 500° C. and 1200° C.in a forming gas to yield non-stoichiometric nanopowders. The powdersare pressed into discs, sintered, and coated with a cermet pastecomprising equal parts silver and a stoichiometric nanoscale form of thestarting powder. Platinum leads are then attached to the cermet paste.Preferably, the cermet paste comprises silver and a non-stoichiometricversion of the starting powder. The starting powder may beyttria-stabilized cubic zirconia, other metal oxides, a perovskitematerial, or another group IV oxide. This invention also includes theimproved energy and ion conducting device produced by this method. Inaddition, it includes an ion and energy conducting device wherein theion conductor is produced from nanostructured beta alumina, NASICON,lithium nitride, LISICON, silver iodide, Rb₄Cu₁₆I₇Cl₁₃, a polymer, or aperovskite.

In another aspect, this invention includes an improved dopant forsemiconductor materials where the dopant comprises a non-stoichiometricnanocrystalline powder. The grain size of the non-stoichiometricnanocrystalline powder may be less than 80 nm, preferably 40 nm, andmore preferably 10 nm. The non-stoichiometric nanocrystalline powder mayinclude one or more materials selected from the group comprisingTa_(2/3)O_(0.9), Nb_(2/5)O_(0.74), NiO_(0.98), Mn_(1/2)O_(0.9),Bi_(2/3)O_(0.45), Cu_(1.9)O, TiO_(1.1), SiO_(1.55), andV_(2/5)O_(0.975).

Briefly stated, the present invention is directed to inks based on novelnanofillers that enhance a wide range of properties. In another aspect,the present invention is directed to methods for preparingnanocomposites that enable nanotechnology applications offering superiorfunctional performance. In an example method, nanofillers and asubstance having a polymer are mixed. Both low-loaded and highly-loadednanocomposites are contemplated. Nanoscale coated and un-coated fillersmay be used. Nanocomposite films may be coated on substrates.

In one aspect, the invention comprises a nanostructured filler,intimately mixed with a matrix to form a nanostructured composite. Atleast one of the nanostructured filler and the nanostructured compositehas a desired material property which differs by at least 20% from thesame material property for a micron-scale filler or a micron-scalecomposite, respectively. The desired material property is selected fromthe group consisting of refractive index, transparency to light,reflection characteristics, resistivity, permittivity, permeability,coercivity, B—H product, magnetic hysteresis, breakdown voltage, skindepth, curie temperature, dissipation factor, work function, band gap,electromagnetic shielding effectiveness, radiation hardness, chemicalreactivity, thermal conductivity, temperature coefficient of anelectrical property, voltage coefficient of an electrical property,thermal shock resistance, biocompatibility and wear rate.

The nanostructured filler may comprise one or more elements selectedfrom the s, p, d, and f groups of the periodic table, or it may comprisea compound of one or more such elements with one or more suitableanions, such as aluminum, antimony, boron, bromine, carbon, chlorine,fluorine, germanium, hydrogen, indium, iodine, nickel, nitrogen, oxygen,phosphorus, selenium, silicon, sulfur, or tellurium. The matrix may be apolymer (e.g., poly(methyl methacrylate), poly(vinyl alcohol),polycarbonate, polyalkene, or polyaryl), a ceramic (e.g., zinc oxide,indium-tin oxide, hafnium carbide, or ferrite), or a metal (e.g.,copper, tin, zinc, or iron). Loadings of the nanofiller may be as highas 95%, although loadings of 80% or less are preferred. The inventionalso comprises devices which incorporate the nanofiller (e.g.,electrical, magnetic, optical, biomedical, and electrochemical devices).

Another aspect of the invention comprises a method of producing acomposite, comprising blending a nanoscale filler with a matrix to forma nanostructured composite. Either the nanostructured filler or thecomposite itself differs substantially in a desired material propertyfrom a micron-scale filler or composite, respectively. The desiredmaterial property is selected from the group consisting of refractiveindex, transparency to light, reflection characteristics, resistivity,permittivity, permeability, coercivity, B—H product, magnetichysteresis, breakdown voltage, skin depth, curie temperature,dissipation factor, work function, band gap, electromagnetic shieldingeffectiveness, radiation hardness, chemical reactivity, thermalconductivity, temperature coefficient of an electrical property, voltagecoefficient of an electrical property, thermal shock resistance,biocompatibility, and wear rate. The loading of the filler does notexceed 95 volume percent, and loadings of 80 volume percent or less arepreferred.

The composite may be formed by mixing a precursor of the matrix materialwith the nanofiller, and then processing the precursor to form a desiredmatrix material. For example, the nanofiller may be mixed with amonomer, which is then polymerized to form a polymer matrix composite.In another embodiment, the nanofiller may be mixed with a matrix powdercomposition and compacted to form a solid composite. In yet anotherembodiment, the matrix composition may be dissolved in a solvent andmixed with the nanofiller, and then the solvent may be removed to form asolid composite. In still another embodiment, the matrix may be a liquidor have liquid like properties.

Yet another aspect of the invention is to prepare nanofillers for inksand dopants including pastes and slurries thereof. These pastes andslurries are then utilized to print nanoscale layers and structures.

Many nanofiller compositions are encompassed within the scope of theinvention, including nanofillers comprising one or more elementsselected from the group consisting of actinium, aluminum, arsenic,barium, beryllium, bismuth, cadmium, calcium, cerium, cesium, cobalt,copper, dysprosium, erbium, europium, gadolinium, gallium, gold,hafnium, hydrogen, indium, iridium, iron, lanthanum, lithium, magnesium,manganese, mendelevium, mercury, molybdenum, neodymium, neptunium,nickel, niobium, osmium, palladium, platinum, potassium, praseodymium,promethium, protactinium, rhenium, rubidium, scandium, silver, sodium,strontium, tantalum, terbium, thallium, thorium, tin, titanium,tungsten, vanadium, ytterbium, yttrium, zinc, and zirconium.

“Domain size” as that term is used herein, refers to the minimumdimension of a particular material morphology. In the case of powders,the domain size is the grain size. In the case of whiskers and fibers,the domain size is the diameter. In the case of plates and films, thedomain size is the thickness.

As used herein, a “nanostructured powder” is one having a domain size ofless than 100 nm, or alternatively, having a domain size sufficientlysmall that a selected material property is substantially different fromthat of a micron-scale powder, due to size confinement effects (e.g.,the property may differ by 20% or more from the analogous property ofthe micron-scale material). Nanostructured powders often advantageouslyhave sizes as small as 50 nm, 30 nm, or even smaller. Nanostructuredpowders may also be referred to as “nanopowders” or “nanofillers.” Ananostructured composite is a composite comprising a nanostructuredphase dispersed in a matrix.

As it is used herein, the term “agglomerated” describes a powder inwhich at least some individual particles of the powder adhere toneighboring particles, primarily by electrostatic forces, and“aggregated” describes a powder in which at least some individualparticles are chemically bonded to neighboring particles.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described with reference to the several figures of thedrawing, in which,

FIG. 1 is a diagram of a nanostructured filler coated with a polymer;

FIG. 2 portrays an X-ray diffraction (XRD) spectrum for thestoichiometric indium tin oxide powder of Example 1;

FIG. 3 is a scanning electron microscope (SEM) micrograph of thestoichiometric indium tin oxide powder of Example 1; and

FIG. 4 is a diagram of the nanostructured varistor of Example 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Non-stoichiometric substances in this invention are envisioned assubstances that bridge between the artificial classification ofsubstances—i.e. metals, alloys, oxides, carbides, nitrides, borides,sulfides, chalcogenides, silicides, etc. For example, while tin (Sn) isa metal, tin oxide (SnO₂) is an oxide ceramic. Non-stoichiometric tinoxide is then a form of a substance that transitions the properties ofmetallic tin to ceramic tin oxide. For example, non-stoichiometric tinoxides can be prepared with composition such as SnO_(0.04), SnO_(0.14),SnO_(0.24), SnO_(0.34), SnO_(0.44), SnO_(0.54), SnO_(0.64), SnO_(0.74),SnO_(0.84), and SnO_(0.94). The physical, thermal, chemical, and otherproperties of tin and tin oxide are very different, and the propertiesof non-stoichiometric tin oxide are anticipated to be very different andunique when compared with both metallic tin and ceramic tin oxide. Thepresence of vacancies in SnO_(x) is anticipated to lead to higherconductivities, novel catalytic properties, novel structural properties,novel magnetic properties, faster sintering, and other desirablecommercial performance. A preferred embodiment is to use a submicronnon-stoichiometric form. A more preferred embodiment is to use ananoscale non-stoichiometric form. It is important to note that thenon-stoichiometric form can be converted to a stoichiometric form if andwhen desired. Thus, the beneficial properties of non-stoichiometricforms can be utilized in some applications during processing, whileleaving the flexibility for use of either a stoichiometric or anon-stoichiometric form in the final product.

Another illustration, without limiting the scope of this invention, isthe non-metal boron and the ceramic boron nitride. In stoichiometricform, boron is B, and the ceramic boron nitride is BN. These twomaterials have very different molecular orbitals and different physical,thermal, chemical, optical, catalytic, structural, and other properties.Additionally, it is easier to process boron than boron nitride.Illustrative but not limiting forms of non-stoichiometric boron nitrideinclude BN_(0.025), BN_(0.125), BN_(0.225), BN_(0.325), BN_(0.425),BN_(0.525), BN_(0.625), BN_(0.725), BN_(0.825), BN_(0.925). It isanticipated that nanoscale forms of these non-stoichiometric BN_(x) willyield novel electrical and electronic properties, novel catalyticproperties, novel structural properties, novel magnetic properties,faster sintering, and other desirable commercial performance. Onceagain, a preferred embodiment is to use a submicron non-stoichiometricform. A more preferred embodiment is to use a nanoscalenon-stoichiometric form. Once again, it is important to note that thenon-stoichiometric form can be converted to a stoichiometric form if andwhen desired. Thus, the beneficial properties of non-stoichiometricforms can be utilized in some applications during processing, whileleaving the flexibility for use of either a stoichiometric or anon-stoichiometric form in the final product.

Yet another illustration, without limiting the scope of this invention,is metallic titanium and the ceramic titanium carbide. In stoichiometricform, metallic titanium is Ti, and ceramic titanium carbide is TiC.These two materials have very different molecular orbitals and differentphysical, thermal, chemical, optical, catalytic, structural, and otherproperties. It is easier to process metals than ceramics, and theductilities of metals are very different than those of ceramics.Illustrative but not limiting forms of non-stoichiometric titaniumcarbide include TiC_(0.05), TiC_(0.15), TiC_(0.25), TiC_(0.35),TiC_(0.45), TiC_(0.55), TiC_(0.65), TiC_(0.75), TiC_(0.85), TiC_(0.95).It is anticipated that nanoscale forms of nonstoichiometric TiC_(x) willyield novel electrical and electronic properties, novel catalyticproperties, novel structural properties, novel magnetic properties,faster sintering, and other desirable commercial performance. Onceagain, a preferred embodiment is to use a submicron non-stoichiometricform. A more preferred embodiment is to use a nanoscalenon-stoichiometric form. Once again, it is important to note that thenon-stoichiometric form can be converted to a stoichiometric form if andwhen desired. Thus, the beneficial properties of non-stoichiometricforms can be utilized in some applications during processing, whileleaving the flexibility for use of either a stoichiometric or anon-stoichiometric form in the final product.

A further illustration, without limiting the scope of this invention, isthe nickel iron alloy and the ceramic nickel ferrite. In stoichiometricform, nickel iron alloy is NiFe, and ceramic nickel ferrite is NiFe₂O₄.These two materials have very different molecular orbitals and differentphysical, thermal, chemical, optical, catalytic, structural, and otherproperties. It is easier to process alloys than ceramics, and theductilities of alloys are very different than those of ceramics.Illustrative but not limiting forms of non-stoichiometric nickel ferriteinclude NiFe₂O_(3.91), NiFe₂O_(3.71), NiFe₂O_(3.51), NiFe₂O_(3.31),NiFe₂O_(3.11), NiFe₂O_(2.91), NiFe₂O_(2.71), NiFe₂O_(2.51),NiFe₂O_(2.31),NiFe₂O_(2.11), NiFe₂O_(1.91), NiFe₂O_(1.71),NiFe₂O_(1.51), NiFe₂O_(1.31), NiFe₂O_(1.11), NiFe₂O_(0.91),NiFe₂O_(0.71), NiFe₂O_(0.51), NiFe₂O_(0.31), NiFe₂O_(0.11),NiFe_(1.8)O₄, NiFe_(0.8)O₄, Ni_(0.9)Fe₂O_(3.9),Ni_(0.9)Fe₂O₄, andNi_(0.4)Fe₂O₄. It is anticipated that nanoscale forms ofnon-stoichiometric nickel ferrite will yield novel electrical andelectronic properties, novel catalytic properties, novel structuralproperties, novel magnetic properties, faster sintering, and otherdesirable commercial performance. Once again, a preferred embodiment isto use a submicron non-stoichiometric form. A more preferred embodimentis to use a nanoscale non-stoichiometric form. Once again, it isimportant to note that the non-stoichiometric form can be converted to astoichiometric form if and when desired. Thus, the beneficial propertiesof non-stoichiometric forms can be utilized in some applications duringprocessing, while leaving the flexibility for use of either astoichiometric or a non-stoichiometric form in the final product.

Nanostructured materials have small grain sizes and high interfacialareas. Nanostructured materials can be prepared by methods such as thosetaught by us in commonly assigned U.S. Pat. No. 5,788,738 and otherssuch as U.S. Pat. Nos. 5,486,675, 5,447,708, 5,407,458, 5,219,804,5,194,128, 5,064,464, all of which are incorporated herein by reference.Relatively high surface area and small grain size makes nanopowderscommercially suitable for processing into non-stoichiometric forms.

The material compositions to be used in the presently claimed inventionare nanostructured non-stoichiometric substances, i.e. materials whosedomain size have been engineered to sub-micron levels, preferably tonanoscale levels (<100 nm) where domain confinement effects becomeobservable, modifying the properties of the materials. The scope of thisinvention excludes non-stoichiometry that results from thermodynamicallyfavored defect structure.

Nanostructured materials (nanomaterials) are a novel class of materialswhose distinguishing feature is that their average grain size or otherdomain size is within a size range where a variety of confinementeffects dramatically change the properties of the material. A propertywill be altered when the entity or mechanism responsible for thatproperty is confined within a space smaller than the critical lengthassociated with that entity or mechanism. Some illustrations of suchproperties include but are not limited to electrical conductivity,dielectric constant, dielectric strength, dielectric loss, polarization,permittivity, critical current, superconductivity, piezoelectricity,mean free path, curie temperature, critical magnetic field,permeability, coercive force, magnetostriction, magnetoresistance, hallcoefficient, BHmax, critical temperature, melting point, boiling point,sublimation point, phase transformation conditions, vapor pressure,anisotropy, adhesion, density, hardness, ductility, elasticity,porosity, strength, toughness, surface roughness, coefficient of thermalexpansion, thermal conductivity, specific heat, latent heat, refractiveindex, absorptivity, emissivity, dispersivity, scattering, polarization,acidity, basicity, catalysis, reactivity, energy density, activationenergy, free energy, entropy, frequency factor, environmental benigness,bioactivity, biocompatibility, and thermal and pressure coefficients ofproperties. The importance of nanostructured materials to this inventioncan be illustrated by considering the example of the mean free path ofelectrons, which is a key determinant of a material's resistivity. Themean free path in conventional materials and resistivity are related by:ρ=mv _(E) /nq ²λwhere,

ρ: resistivity

m: mass of electron

v_(E): Fermi energy

n: number of free electrons per unit volume in material

q: charge of electron

λ: mean free path of electron

This equation assumes that the resistivity in the material is determinedin part by the mean free path of electrons and that the electrons have afree path in the bulk. In nanostructured materials, the domain size isconfined to dimensions less than the mean free path and the electronmeets the interface of the domain before it transverses a path equal tothe mean free path. Thus, if the material's domain size is confined to asize less than the mean free path, this equation is no longer valid. Ina simplistic model, one could replace λ with the domain size, but thatreplacement ignores the fact that confinement can also affect “n” andother fundamental properties. This insight suggests that unusualproperties may be expected from devices prepared from materials with adomain size less than the mean free path of electrons.

While the above argument is discussed in light of mean free path, it isimportant to note that the domain confinement effect can be observedeven when the domain size is somewhat larger than the mean free pathbecause: (a) “mean” free path is a statistical number reflecting a meanof path lengths statistically observed in a given material, and (b) invery finely divided materials, the interface volume is significant andall the free electrons do not see the same space; electrons closer tothe interface interact differently than those localized in the center ofthe domain.

The significance of using nanostructured materials can be furtherappreciated if the conductivity of semiconducting oxides is consideredas shown in the equation for conductivity from hopping mechanism:σ=P _(a) P _(b)2e ² /ckTV[exp(q/kT)]where,

σ: conductivity

P_(a), P_(b): probabilities that neighboring sites are occupied bydesirable cations

e: electronic charge

n: frequency factor

k: Boltzmann's constant

T: temperature

q: activation energy

c: unit cell dimension

v: hopping velocity

The frequency factor and activation energy are a strong function of themicrostructure confinement and non-stoichiometry; therefore, theconductivity of the same material can be very different innanostructured non-stoichiometric form when compared with naturallyoccurring bulk crystal form of the substance.

As the phrase is used herein, “nanostructured materials” are consideredto be materials with a domain size less than 5 times the mean free pathof electrons in the given material, preferably less than the mean freepath of electrons. Alternatively, the domain size may be less than 500nanometers, and preferably less than 100 nanometers. Nanostructuredmaterials also include substances with a mean domain size less than orequal to the domain size below which the substance exhibits 10% or morechange in at least one property of the said substance when the domainsize is changed by a factor of 2, everything else remaining the same.Furthermore, the term nanostructured materials incorporates zerodimensional, one dimensional, two dimensional, and three dimensionalmaterials.

Nanopowders in this invention are nanostructured materials wherein thedomain size is the powder's grain size. For the scope of the invention,the term nanopowders includes powders with an aspect ratio differentthan one, and more specifically powders that satisfy the relation:10⁰<aspect ratio<10⁶.

Submicron materials in this disclosure are materials with mean grainsize less than 1 micrometer.

Non-stoichiometric materials are metastable materials, which have acomposition that is different than that required for stoichiometricbonding between two or more elements. For example, stoichiometrictitania can be represented as TiO₂ while non-stoichiometric titania canbe represented as TiO_(2-x)(TiO_(1.8) and TiO_(1.3) would be twospecific examples of non-stoichiometric titania). Stoichiometric bondingbetween two or more elements indicates that charge balance is achievedamong the said elements. In general, a stoichiometric material is givenby:M_(n)Z_(p)

where, Z can be any element from the p, d, and f groups of the periodictable (illustrations include: C, O, N, B, S, H, Se, Te, In, Sb, Al, Ni,F, P, Cl, Br, I, Si, and Ge). M can be any element that can lower itsfree energy by chemically bonding with Z (illustrations include: Ti, Mn,Fe, Ni, Zn, Cu, Sr, Y, Zr, Ta, W, Sc, V, Co, In, Li, Hf, Nb, Mo, Sn, Sb,Al, Ce, Pr, Be, Np, Pa, Gd, Dy, Os, Pt, Pd, Ag, Eu, Er, Yb, Ba, Ga, Cs,Na, K, Mg, Pm, Pr, Ni, Bi, Tl, Ir, Rb, Ca, La, Ac, Re, Hg, Cd, As, Th,Nd, Th, Md, and Au), where n and p, integers for stoichiometric bondingbetween M and Z, are greater than or equal to 1.

A non-stoichiometric form of the same material may then be given by:M_(nx)Z_(py)

where 0<x<n and 0<y<p.

An alternative representation of a non-stoichiometric material isM_(n/p)Z_(1-x), where 0<x<1. In this invention, the preferred rangeincludes 0.01<x<0.99, preferably 0.02<x<0.98, and more preferably0.05<x<0.95.

Empirical methods may also be used to determine whether a material isnon-stoichiometric. Some embodiments of such methods are as follows:

1. Heat a stoichiometric form of the material and the material beingevaluated for non-stoichiometry separately in a reactive atmosphere(e.g., oxygen, if oxygen non-stoichiometry is being ascertained) to 0.5times the melting point of the material; monitor the weight change perunit sample weight. The material being evaluated is non-stoichiometricif its weight change per unit sample weight is greater than either 1% ofthe weight of the sample or 25% of the weight change in the sample ofstoichiometric form.

2. Alternatively, perform a quantitative elemental analysis on thematerial; if the relative ratio of the elements yields an “x” that isnot an integer (and the relative ratio deviates by more than 1%,preferably more than 2% and more preferably by more than 5%), thematerial is non-stoichiometric.

3. Alternatively, measure the properties of the material in the idealstoichiometric form and compare this with the substance being evaluatedfor non-stoichiometry; if any property of the material, or thetemperature coefficient of any property varies by more than 10% betweenthe two substances, everything else remaining the same, the substancebeing evaluated is non-stoichiometric.

These empirical methods will not work universally and may givemisleading results because some materials decompose with heating, andanalytical techniques are prone to statistical errors. These empiricalmethods should not be considered limiting and other methods ofestablishing “x” fall within the scope of the invention.

In the M_(n-x)Z_(p-y) representation discussed above, non-stoichiometricmaterials may have more than one “M,” more than one “Z,” or both. Inthis case, the representation can be π_(Ij)(M_(I,ni-xi)Z_(j,pj,yj)),where π_(Ij) represents a multiplicity in i and j. A material is thennon-stoichiometric if the relative ratio of any M or any Z or anycombination is different by more than 2.5% than what is needed fortheoretical bonding between the said elements. Some illustrations ofthis, without limiting the scope of the invention, would benon-stoichiometric compositions such as BaTiO_(3-x), Ba_(1-x)TiO₃,NiFe₂O_(3-x), Ni_(1-x)Fe₂O₃, NiFe₂O₃Ni_(1-x), PbZrTiO_(3-x), TiCN_(1-x),and TiC_(1-x)N. It is also important to note that, for the scope of thisinvention, non-stoichiometric substances include substances producedwhen one or more of Z and/or M in π_(Ij)(M_(I,ni-xi)Z_(j,pj,yj)) isreplaced partially or completely with additional elements, i.e., Z_(s)or M_(s). An example of this would be stoichiometric MnFe₂O₄, which,after processing, becomes MnFe₂O_(3.5)N_(0.1) or MnFe₂O_(3.1)B_(0.3).Another example of this is stoichiometric TiB₂ which after processingbecomes TiB_(1.5)N_(0.3) or TiB_(1.1)C_(0.2).

It is important to note that all naturally produced and artificiallyproduced materials have defects because defects are thermodynamicallyfavored. Such thermodynamically favored defects can lead to smallamounts of inherent non-stoichiometry in substances. The presentlyclaimed non-stoichiometric materials differ from such naturally producedand artificially produced substances in the following:

This invention excludes from its scope the non-stoichiometry thatnaturally results from the randomly occurring thermodynamic defects in abulk crystal of the theoretical stoichiometry which are typically on theorder of a few hundred parts per million. Preferred levels ofnon-stoichiometry according to the invention are those whichsignificantly exceed equilibrium levels. Alternatively, the preferredranges include 0.01<x<0.99, preferably 0.02<x<0.98, and more preferably0.05<x<0.95.

This invention teaches the methods for engineering unusualnon-stoichiometric compositions, and provides motivation to harnesstheir unusual properties. The invention stabilizes and makesnon-stoichiometry commercially attractive by engineering nanostructurein the non-stoichiometric material. It should be noted thatnanostructured non-stoichiometric substances are anticipated to haveinterfacial stresses that play an important role in determining theunique properties and unusual thermodynamic nature of these substances,thereby yielding materials with unprecedented compositions of matter andperformance.

In the presently claimed invention, the scope of the invention includesnanostructured materials with a domain size less than 5 times the meanfree path of electrons in the given material, preferably less than themean free path of electrons. In the event that it is difficult totheoretically compute the mean free path of the non-stoichiometricmaterial under consideration, it is recommended that the domain size beless than 500 nanometers, preferably less than 100 nanometers. If it isdifficult to measure the grain size or the grain size changes during theproduction or use of the device, the scope of the invention includesnon-stoichiometric materials with a domain size that exhibit 10% or morechange in at least one property of the said substance when the domainsize is changed by a factor of 2, everything else remaining same.

A very wide range of material properties and product performance can beengineered by the practice of the invention. For example, unusual orimproved electrical, electronic, magnetic, optical, electrochemical,chemical, catalytic, thermal, structural, biomedical, surfaceproperties, and combinations thereof can be obtained or varied over awider range using nanostructured non-stoichiometric substances than ispossible using prior art stoichiometric substances. Such benefits canmotivate use of these materials in pellet or film type or multilayertype devices and products.

Nanostructured non-stoichiometric substances can be used as fillers tolower or raise the effective resistivity, effective permittivity, andeffective permeability of a polymer or ceramic matrix. While theseeffects are present at lower loadings, they are expected to be mostpronounced for filler loadings at or above the percolation limit of thefiller in the matrix (i.e. at loadings sufficiently high that electricalcontinuity exists between the filler particles). Other electricalproperties which could potentially be engineered include breakdownvoltage, skin depth, curie temperature, temperature coefficient ofelectrical property, voltage coefficient of electrical property,dissipation factor, work function, band gap, electromagnetic shieldingeffectiveness and degree of radiation hardness. Nanostructurednon-stoichiometric fillers can also be used to engineer magneticproperties such as the coercivity, BH product, hysteresis, and shape ofthe BH curve of a matrix. Even when non-stoichiometric substances areused in monolithic form, these unique electrical, magnetic, andelectronic properties hold significant commercial interest.

Other important characteristics of an optical material are itsrefractive index and transmission and reflection characteristics.Nanostructured non-stoichiometric substances can be used to producecomposites with refractive indices engineered for a particularapplication. Gradient lenses produced from nanostructurednon-stoichiometric composites are anticipated to reduce or eliminate theneed for polishing lenses. The use of nanostructured non-stoichiometricsubstances are anticipated to also help filter specific wavelengths.Furthermore, an expected advantage of nanostructured non-stoichiometricsubstances in optical applications is their enhanced transparencybecause the domain size of nanostructured fillers ranges from about thesame as to more than an order of magnitude less than visible wavelengthsof light. Photonic applications where specific wavelengths of light areprocessed are anticipated to utilize the unique optical properties ofnon-stoichiometric substances.

The high surface area and small grain size of non-stoichiometricsubstances and their composites make them excellent candidates forchemical and electrochemical applications. When used to form electrodesfor electrochemical devices, these materials are expected tosignificantly improve performance, for example, by increasing powerdensity in batteries and reducing minimum operating temperatures forsensors. Nanostructured non-stoichiometric substances are also expectedto modify the chemical properties of composites. These uniquenon-stoichiometric substances are anticipated to be catalytically moreactive and to provide more interface area for interacting with diffusivespecies. They are anticipated to provide the materials needed in ourcommonly assigned patent application Ser. No.09/165,439 on a method andprocess for transforming chemical species which utilizes electromagneticfields, and which is incorporated by reference herein. Such substancesare anticipated to also modify chemical stability and mobility ofdiffusing gases. Furthermore, nanostructured non-stoichiometricsubstances are anticipated to enhance the chemical properties ofpropellants and fuels or safety during storage and transportation orboth.

Many nanostructured non-stoichiometric substances have a domain sizecomparable to the typical mean free path of phonons at moderatetemperatures. These non-stoichiometric substances are anticipated tohave dramatic effects on the thermal conductivity and thermal shockresistance of matrices and products into which they are incorporated.Potential applications include fluids used for heat transfer.

Nanostructured non-stoichiometric substances-which may be utilized incoated and uncoated form-and composites derived thereof are alsoexpected to have significant value in biomedical applications for bothhumans and animals. For example, the small size of nanostructurednon-stoichiometric substances will make them readily transportablethrough pores and capillaries. This suggests that the non-stoichiometricsubstances will be of use in developing novel time-release drugs andmethods of administration and delivery of drugs, markers, and medicalmaterials. A polymer coating can be utilized either to makewater-insoluble fillers into a form that is water soluble, or to makewater-soluble fillers into a form that is water insoluble. A polymercoating on the filler may also be utilized as a means to timedrug-release from a nanoparticle. A polymer coating may further be usedto enable selective filtering, transfer, capture, and removal of speciesand molecules from blood into the nanoparticle.

The invention can be used to prepare propellants and fuels that aresafer to store, transport, process, and use. The non-stoichiometry canalso provide increased energy density or oxidant or both.

The invention can be used to produce superior or more affordablecatalysts for the synthesis of currently used and novel organiccompounds, inorganic compounds, organometallic compounds,pharmaceuticals, polymers, petrochemicals, reagents, metallurgicalproducts, and combinations thereof. The invention can also be used toproduce superior or more affordable catalysts for environmental andother applications that currently or in the future can benefit fromcatalysis. Similarly, the invention can be used to produce superior ormore affordable phosphors for monochromatic and color displayapplications.

A nanoparticulate non-stoichiometric filler for biomedical operationsmight be a carrier or support for a drug of interest, participate in thedrug's functioning, or might even be the drug itself. Possibleadministration routes include oral, topical, and injection routes.Nanoparticulates and nanocomposites are anticipated to also have utilityas markers or as carriers for markers. Their unique properties,including high mobility and unusual physical properties, make themparticularly well-adapted for such tasks.

In some examples of biomedical functions, magnetic non-stoichiometricnanoparticles such as ferrites may be utilized to carry drugs to aregion of interest, where the particles may then be concentrated using amagnetic field. Photocatalytic non-stoichiometric nanoparticles can beutilized to carry drugs to a region of interest and then photoactivated.Thermally sensitive non-stoichiometric nanoparticles can similarly beutilized to transport drugs or markers or species of interest and thenthermally activated in the region of interest. Radioactivenon-stoichiometric nanoparticulate fillers are anticipated to haveutility for chemotherapy. Nanoparticles suitably doped with genetic,cultured, or other biologically active materials may be utilized in asimilar manner to deliver therapy in target areas. Nanocompositeparticles may be used to assist in concentrating the particle and thenproviding therapeutic action. To illustrate, magnetic and photocatalyticnanoparticles may be formed into a composite, administered to a patient,concentrated in area of interest using a magnetic field, and finallyactivated using photons directed to the concentrated particles. Asmarkers, coated or uncoated non-stoichiometric nanoparticulate fillersmay be used for diagnosis of medical conditions. For example, fillersmay be concentrated in a region of the body where they may be viewed bymagnetic resonance imaging or other techniques. In all of theseapplications, the possibility exists that nanoparticulates can bereleased into the body in a controlled fashion over a long time period,by implanting a nanocomposite material having a bioabsorbable matrix,which slowly dissolves in the body and releases its embedded filler.

Other benefits disclosed in co-owned U.S. Pat. No. 6,228,904 onnanostructured fillers, and which is incorporated by reference hereinand recited below, are applicable to the non-stoichiometric materials ofthe present invention.

Prior art filler materials for polymeric composites are usually powderswith an average dimension in the range of 10-100 μm. Thus, each fillerparticle typically has on the order of 10¹⁵-10¹⁸ atoms. In contrast thetypical polymer chain has on the order of 10³-10⁹ atoms. While the artof precision manufacturing of polymers at molecular levels iswell-developed, the knowledge of precision manufacturing of fillermaterials at molecular levels has remained largely unexplored.

The number of atoms in the filler particles of the invention(hereinafter called “nanostructured filler” or “nanofiller”) is on theorder of or significantly less than the number of atoms in the polymermolecules, e.g., 10²-10¹⁰. Thus, the filler particles are comparable insize or smaller than the polymer molecules, and therefore can bedispersed with orders of magnitude higher number density. Further, thefillers may have a dimension less than or equal to the critical domainsizes that determine the characteristic properties of the bulkcomposition; thus, the fillers may have significantly different physicalproperties from larger particles of the same composition. This in turnmay yield markedly different properties in composites using nanofillersas compared to the typical properties of conventional polymercomposites.

These nanostructured filler materials may also have utility in themanufacture of other types of composites, such as ceramic- ormetal-matrix composites. Again, the changes in the physical propertiesof the filler particles due to their increased surface area andconstrained domain sizes can yield changes in the achievable propertiesof composites.

The nanofillers of the invention can be inorganic, organic, or metallic,and may be in the form of powders, whiskers, fibers, plates or films.The fillers represent an additive to the overall composite composition,and may be used at loadings of up to 95% by volume. The fillers may haveconnectivity in 0, 1, 2, or 3 dimensions. Fillers may be produced by avariety of methods, such as those described in U.S. Pat. Nos. 5,486,675;5,447,708; 5,407,458; 5,219,804; 5,194,128; and 5,064,464. Particularlypreferred methods of making nanostructured fillers are described in U.S.patent application Ser. No. 09/046,465, by Bickmore, et al., filed Mar.23, 1998, now U.S. Pat. No. 5,984,997 and Ser. No. 08/706,819, byPirzada, et al., filed Sep. 3, 1996, now U.S. Pat. No. 5,851,507 both ofwhich are incorporated herein by reference.

A method of making nanostructured fillers is described in commonly ownedU.S. patent application Ser. No. 09/046,465, by Bickmore, et al., filedMar. 23, 1998, now U.S. Pat. No. 5,984,997 which is herewith recited.For example, if a doped complex of composition:d₁-M₁M₂Xis desired, then according to the invention, one should preparesolutions or suspensions of dopant d₁, metals M₁ and M₂, and anion X,where M₁ and M₂ are selected from the s, p, f, and d groups of theperiodic table, and X is selected from the p group of the periodictable. Solutions or suspensions may be prepared, for example, by mixingsolutions containing each of the constituent elements of the desiredpowder. Elements dopant d₁, metals M₁ and M₂ are selected from the groupconsisting of the s group, p group, d group, or f group of the periodictable, and X is selected from the group consisting of carbon, nitrogen,oxygen, boron, phosphorus, sulfur, chalcogens, and halogens.

It will be understood by those skilled in the art that powderscomprising larger numbers of dopants, metals, and anions can also beproduced by the same methods. In particular, polymetallic materialscomprising at least three metals and at least one anion can be produced.These materials are useful in the manufacture of capacitors, inductors,varistors, resistors, piezo-devices, thermistors, thermoelectricdevices, filters, connectors, magnets, ion-conducting devices, sensors,fuel cells, catalysts, optics, photonic devices, lasers, tooling bits,armor, superconductors, inks, and pigments, for example. Prior artpolymetallic powders are limited to sizes in excess of 300 nm, andmostly to sizes in excess of 1 micrometer. By the methods of theinvention, solid or porous polymetallic nanopowders can be made, withsizes less than 250 nm, and preferably less than 100 nm. Furthermore, bythe methods of the invention, nano-whiskers and nano-rods can beproduced with aspect ratios of 25 or less, having a minimum dimension ofless than 250 nm, and preferably less than 100 nm. At this scale, sizeconfinement effects can come into play for many polymetallic powders.

While this invention does not limit itself to a specific cation oranion, it is desirable to use anions and cations that are either part ofthe final product or completely volatile. The final products are notlimited to ionic materials, and include covalent and mixedionic-covalent materials such as carbides, borides, nitrides, sulfides,oxycarbides, oxynitrides, oxyborides and oxysulfides. Illustrativeformulations, but not exhaustive, then are nitrate, nitrites, nitriles,nitrides, carbonates, bicarbonates, hydroxides, cyanos, organometallics,carboxylates, amines, and amides.

In one aspect of commonly owned U.S. patent application Ser. No.09/046,465, by Bickmore, et al., filed Mar. 23, 1998, now U.S. Pat. No.5,984,997 which is herewith recited, the invention comprises a method ofcontinuously producing fine powders of complex inorganic compositions,including, but not limited to, carbides, nitrides, oxides,chalcogenides, halides, phosphides, borides, and combinations thereof bycombustion of emulsions. By varying the characteristics of the initialemulsion, the size, shape, surface area, morphology, surfacecharacteristics, surface composition, distribution, and degree ofagglomeration of the final powder may be controlled. And, in conjunctionwith varying combustion conditions, the product chemistry may be variedto obtain non-stoichiometric, reduced oxide, or mixed anion materials.Examples of this embodiment include the use of non-stoichiometric flamesor reducing gases such as hydrogen, forming gas, or ammonia. It is anadvantage of these aspects of the invention that the method can use lowcost, safe, readily available and environmentally benign precursors toproduce fine powders. In a preferred embodiment, the method ensures highyield and high selectivity, including harvesting 95% or more of the finepowder produced. In another embodiment, the method prevents the damageof the fine powders during and after their synthesis.

In another aspect, the invention includes multimetallic powders having amedian particle size of less than 5 micron and a standard deviation ofparticle size of less than 100 nm. In preferred embodiments, the medianparticle size is less than 100 nm and the standard deviation of particlesize is less than 25 nm, and in further preferred embodiments, themedian particle size is less than 30 nm and the standard deviation ofparticle size is less than 10 nm. The multimetallic powders include atleast two elements selected from the s group, p group, d group, and fgroup of the periodic table (e.g., aluminum, antimony, barium, bismuth,boron, bromine, cadmium, calcium, carbon, cerium, cesium, chlorine,chromium, cobalt, copper, dysprosium, erbium, europium, gadolinium,gallium, germanium, gold, hafnium, holmium, indium, iodine, iridium,iron, lanthanum, lead, lithium, lutetium, magnesium, manganese,molybdenum, neodymium, nickel, niobium, nitrogen, osmium, oxygen,palladium, phosphorus, platinum, praseodymium, potassium, rhenium,rhodium, rubidium, samarium, scandium, silicon, silver, sodium,strontium, sulfur, tantalum, terbium, thulium, tin, titanium, tungsten,vanadium, ytterbium, yttrium, zinc, and zirconium), and may includethree or more such elements. The powders may be unagglomerated and/orunaggregated. The multimetallic powders may also comprise nanowhiskersand/or nanorods, with aspect ratios in a range of 1-25.

The term “nanopowder” describes a powder whose mean diameter is so smallthat its physical properties are substantially affected by size relatedconfinement effects. Nanopowders usually have a mean diameter less thanor equal to 250 nm, and preferably have a mean diameter less than orequal to 100 nm. More preferably, nanopowders may have a mean diameterless than 50 nm.

The term “aspect ratio” refers to the ratio of the maximum to theminimum dimension of a particle. The term “whisker” refers to anyelongated particle (e.g., a particle having an aspect ratio greater thanone, and preferably at least two). Whiskers may be round or faceted, andmay have varying diameters. “Rods” are substantially cylindricalwhiskers. “Nanowhiskers” and “nanorods” refer to rods and whiskers whosesmallest dimension is so small that their physical properties aresubstantially affected by size related confinement effects. Nanowhiskersand nanorods usually have a minimum dimension less than or equal to 250nm, and preferably have a minimum dimension less than or equal to 100nm. More preferably, these particles may have a minimum dimension lessthan 50 nm.

A distinctive feature of the invention described in commonly owned U.S.patent application Ser. No. 09/046,465, by Bickmore, et al., filed Mar.23, 1998, now U.S. Pat. No. 5,984,997 which is herewith recited, is theuse of emulsion as the vehicle for carrying fuels and metals. Once anemulsion formulation has been established, dopants and other metals canbe readily added to the said emulsion to prepare and vary complexcompositions. It will be understood by those skilled in the art thatpowders comprising larger numbers of dopants, metals, and anions canalso be produced by the same methods. In particular, polymetallicmaterials comprising at least three metals and at least one anion can beproduced. These materials are useful in the manufacture of capacitors,inductors, varistors, resistors, piezo-devices, thermistors,thermoelectric devices, filters, connectors, magnets, ion-conductingdevices, sensors, fuel cells, catalysts, optics, photonic devices,lasers, tooling bits, armor, superconductors, inks, and pigments, forexample. Prior art polymetallic powders are limited to sizes in excessof 300 nm, and mostly to sizes in excess of I micrometer. By the methodsof the invention, solid or porous polymetallic nanopowders can be made,with sizes less than 250 nm, and preferably less than 100 nm.Furthermore, by the methods of the invention, nano-whiskers andnano-rods can be produced with aspect ratios of 25 or less, having aminimum dimension of less than 250 nm, and preferably less than 100 nm.At this scale, size confinement effects can come into play for manypolymetallic powders.

The solutions or suspensions of the invention can be aqueous based ororganic based. While this invention does not limit itself to a specificcation or anion, it is desirable to use anions and cations that areeither part of the final product or completely volatile. The finalproducts are not limited to ionic materials, and include covalent andmixed ionic-covalent materials such as carbides, borides, nitrides,sulfides, oxycarbides, oxynitrides, oxyborides and oxysulfides.Illustrative formulations, but not exhaustive, then are nitrate,nitrites, nitrites, nitrides, carbonates, bicarbonates, hydroxides,cyanos, organometallics, carboxylates, amines, and amides. Once theindividual solutions or suspensions are available, an emulsion isprepared from the solution or suspensions.

A distinctive feature of the invention is the use of emulsion as thevehicle for carrying fuels and metals. Once an emulsion formulation hasbeen established, dopants and other metals can be readily added to thesaid emulsion to prepare and vary complex compositions. The approachhere is that the emulsion formulation(s) and dopants can be storedseparately and then mixed at will to achieve an application-specificcomplex composition. To vary the final composition, the proportion offormulation(s) and dopants can be changed. To illustrate, if twoseparate emulsion formulations are available for preparing M₁O and M₂O,then the composition (M₁)_(0.1)(M₂)_(0.9)O can be prepared by mixing thetwo formulations in 10:90 ratio respectively; on the other hand, if thecomposition (M₁)_(0.9)(M₂)_(0.1)O is desired, it can be prepared bymixing the two formulations in 90:10 ratio respectively. One or moredopants can also be added as desired. For more complex formulations, onecan mix different emulsions and dopants. An advantage of the inventionis that a wide range of complex nanoscale powder compositions can beprepared from a small set of ingredients, that is, emulsionformulation(s) and dopant solutions. Another advantage is that the costof producing specific compositions can be lowered from economiespossible in preparing common ingredients in bulk. Yet another advantageis that emulsions can be prepared from very low-cost, readily availableprecursors. As will be apparent to those skilled in the art, it isimportant to ensure that the emulsions being mixed are compatible. Itwill also be apparent that many emulsions can be prepared for the samemetal—a fact that adds versatility to this invention.

The emulsion may be either polar-in-non-polar (water-in-oil) ornon-polar-in-polar (oil-in-water) or of any other at least temporarilystable type, including polar-in-polar and non-polar-in-non-polar. Somerepresentative stable emulsions are described, for example, inKirk-Othmer, “Emulsions,” Encyclopedia of Chemical Technology, Vol 9,Wiley-Interscience, New York, 1994, which along with the reference citedtherein is herewith incorporated in entirety. While stable emulsions arepreferred, metastable emulsions and temporarily stable emulsions arealso within the scope of the invention. To practice the invention,metastable emulsions and temporarily stable emulsions must be stable fora time at least equal to or greater than the time needed to transportand combust the emulsion.

According to the invention, at least one component of the emulsion actsas a fuel. The fuel component can be part of one of the solution phasesor can be separately added to achieve combustibility. Emulsifying agentsand dispersants may also be added to homogenize or stabilize theemulsion, to enhance combustion, or to achieve a combination of thesecharacteristics.

The emulsions are pumped directly and atomized, or, alternatively,carried in a gas or a mix of gases that do not possess or do notcontribute an element that is not desired in the final composition.Preferred carrier stream gases are nitrogen, air, oxygen, argon, helium,neon, and xenon. It is also within the scope of the invention to includein the carrier stream a reactant such as ammonia gas.

The emulsion is combusted using designs such as, but not limited to,those taught by Khavkin (Combustion System Design, Penn Well Books,Tulsa Okla., 1996) and Fischer (Combustion Engineer's Handbook, G.Newnes Publisher, London, 1961), which are incorporated herein byreference. The combustion can be accomplished using a laminar orturbulent flame, a premixed or diffusion flame, a co-axial or impingingflame, a low-pressure or high-pressure flame, a sub-sonic or sonic orsuper-sonic flame, a pulsating or continuous flame, an externallyapplied electromagnetic field free or externally applied electromagneticfield influenced flame, a reducing or oxidizing flame, a lean or richflame, a secondary gas doped or undoped flame, a secondary liquid dopedor undoped flame, a secondary particulate doped or undoped flame, anadiabatic or non-adiabatic flame, a one-dimensional or two-dimensionalor three-dimensional flame, an obstruction-free or obstructed flame, aclosed or open flame, an externally heated or externally cooled flame, apre-cooled or pre-heated flame, a one burner or multiple burner flame,or a combination of one or more of the above. Usually, combustiontemperatures will be in excess of 600° C., a temperature at whichdiffusion kinetics will be sufficiently fast that a compositionallyuniform powder will be produced. The emulsion can also be a feed toother processes of producing nanoscale powders. Examples include thepowder-formation processes described in copending and commonly assignedU.S. patent application Ser. No. 08/707,341, “Boundary LayerJoule—Thompson Nozzle for Thermal Quenching of High Temperature Vapors,”now U.S. Pat. No. 5,788,738 and Ser. No. 08/706,819, “Integrated ThermalProcess and Apparatus for the Continuous Synthesis of NanoscalePowders,” now U.S. Pat. No. 5,851,507, both of which are incorporatedherein.

A wide variety of nanofiller compositions are possible. Some exemplarycompositions include metals (e.g., Cu, Ag, Ni, Fe, Al, Pd, and Ti),oxide ceramics (e.g., TiO₂, TiO_(2-x), BaFe₂ O₄, dielectriccompositions, ferrites, and manganites), carbide ceramics (e.g., SiC,BC, TiC, WC, WCsub.1-x), nitride ceramics (e.g., Si₃ N₄, TiN, VN, AlN,and Mo₂ N), hydroxides (e.g., aluminum hydroxide, calcium hydroxide, andbarium hydroxide), borides (e.g., AlB₂ and TiB₂), phosphides (e.g., NiPand VP), sulfides (e.g., molybdenum sulfide, titanium sulfide, andtungsten sulfide), silicides (e.g., MoSi₂), chalcogenides (e.g., Bi₂Te₃, Bi₂ Se₃), and combinations of these.

The fillers are immediately mixed with a matrix material, which ispreferably polymeric, buy may also be ceramic, metallic, or acombination of the above. The matrix may be chosen for properties suchas ease of processability, low cost, environmental benignity, commercialavailability, and compatibility with the desired filler. The fillers arepreferably mixed homogeneously into the matrix, but may also be mixedheterogeneously if desired, for example to obtain a composite having agradient of some property. Mixing techniques for incorporating powdersinto fluids and for mixing different powders are well known in the art,and include mechanical, thermal, electrical, magnetic, and chemicalmomentum transfer techniques, as well as combinations of the above.

The viscosity, surface tension, and density of a liquid matrix materialcan be varied for mixing purposes, the preferred values being those thatfavor ease of mixing and that reduce energy needed to mix withoutintroducing any undesirable contamination. One method of mixing is todissolve the matrix in a solvent which does not adversely affect theproperties of the matrix or the filler and which can be easily removedand recovered. Another method is to melt the matrix, incorporate thefiller, and cool the mixture to yield a solid composite with the desiredproperties. Yet another method is to synthesize the matrix in-situ withthe filler present. For example, the nanofiller can be mixed with aliquid monomer, which can then be polymerized to form the composite. Inthis method, the filler may be used as a catalyst or co-catalyst forpolymerization. The mixing may also be accomplished in the solid state,for example by mixing a powdered matrix composition with the filler, andthen compacting the mixture to form a solid composite.

Mixing can be assisted using various secondary species such asdispersants, binders, modifiers, detergents, and additives. Secondaryspecies may also be added to enhance one to more of the properties ofthe filler-matrix composite.

Mixing can also be assisted by pre-coating the nanofiller with a thinlayer of the matrix composition or with a phase that is compatible withthe matrix composition. Such a coated nanoparticle is illustrated inFIG. 1, which shows a spherical nanoparticle 6 and a coating 8. In oneembodiment, when embedding nanofillers in a polymer matrix, it may bedesirable to coat the filler particles with a related monomer. Whenmixing nanofillers into a ceramic matrix, pre-coating can be done byforming a ceramic layer around the nanoscale filler particle during orafter the synthesis of the nanoscale filler, by methods such as partialoxidation, nitridation, carborization, or boronation. In these methods,the nanostructured filler is exposed to a small concentration of aprecursor that reacts with the surface of the filler to form a ceramiccoating. For example, a particle may be exposed to oxygen in order tocreate an oxide coating, to ammonia in order to create a nitridecoating, to borane to create a boride coating, or to methane to create acarbide coating. It is important that the amount of precursor be small,to prevent thermal runaway and consequent conversion of thenanostructured filler into a ceramic particle.

In case of polymer matrix, the filler can be coated with a polymer or amonomer by numerous methods, for example, surface coating in-situ, spraydrying a dispersion of filler and polymer solution, co-polymerization onthe filler surface, and melt spinning followed by milling. A preferredmethod is surface coating in-situ. In this process, the filler is firstsuspended in demineralized water (or another solvent) and thesuspension's pH is measured. The pH is then adjusted and stabilized withsmall addition of acid (e.g., acetic acid or dilute nitric acid) or base(e.g., ammonium hydroxide or dilute sodium hydroxide). The pH adjustmentproduces a charged state on the surface of the filler. Once a desired pHhas been achieved, a coating material (for example, a polymer or otherappropriate precursor) with opposite charge is introduced into thesolvent. This step results in coupling of the coating material aroundthe nanoscale filler and formation of a coating layer around thenanoscale filler. Once the layer has formed, the filler is removed fromthe solvent by drying, filtration, centrifugation, or any other methodappropriate for solid-liquid separation. This technique of coating afiller with another material using surface charge can be used for avariety of organic and inorganic compositions.

When a solvent is used to apply a coating as in the in-situ surfacecoating method described above, the matrix may also be dissolved in thesolvent before or during coating, and the final composite formed byremoving the solvent.

A very wide range of material properties can be engineered by thepractice of the invention. For example, electrical, magnetic, optical,electrochemical, chemical, thermal, biomedical, and tribologicalproperties can be varied over a wider range than is possible using priorart micron-scale composites.

Nanostructured fillers can be used to lower or raise the effectiveresistivity, effective permittivity, and effective permeability of apolymer or ceramic matrix. While these effects are present at lowerloadings, they are expected to be most pronounced for filler loadings ator above the percolation limit of the filler in the matrix (i.e., atloadings sufficiently high that electrical continuity exists between thefiller particles). Other electrical properties which may be engineeredinclude breakdown voltage, skin depth, curie temperature, temperaturecoefficient of electrical property, voltage coefficient of electricalproperty, dissipation factor, work function, band gap, electromagneticshielding effectiveness and degree of radiation hardness. Nanostructuredfillers can also be used to engineer magnetic properties such as thecoercivity, B—H product, hysteresis, and shape of the B—H curve of amatrix.

An important characteristic of optical material is its refractive indexand its transmission and reflective characteristics. Nanostructuredfillers may be used to produce composites with refractive indexengineered for a particular application. Gradient lenses may be producedusing nanostructured materials. Gradient lenses produced fromnanostructured composites may reduce or eliminate the need for polishinglenses. The use of nanostructured fillers may also help filter specificwavelengths. Furthermore, a key advantage of nanostructured fillers inoptical applications is expected to be their enhanced transparencybecause the domain size of nanostructured fillers ranges from about thesame as to more than an order of magnitude less than visible wavelengthsof light.

The high surface area and small grain size of nanofilled composites makethem excellent candidates for chemical and electrochemical applications.When used to form electrodes for electrochemical devices, thesematerials are expected to significantly improve performance, for exampleby increasing power density in batteries and reducing minimum operatingtemperatures for sensors. (An example of the latter effect can be foundin copending and commonly assigned U.S. application Ser. No. 08/739,257,“Nanostructured Ion Conducting Solid Electrolytes,” by Yadav, et al. nowU.S. Pat. No. 5,905,000). Nanostructured fillers are also expected tomodify the chemical properties of composites. These fillers arecatalytically more active, and provide more interface area forinteracting with diffusive species. Such fillers may, for example,modify chemical stability and mobility of diffusing gases. Furthermore,nanostructured fillers may enhance the chemical properties ofpropellants and fuels.

Many nanostructured fillers have a domain size comparable to the typicalmean free path of phonons at moderate temperatures. It is thusanticipated that these fillers may have dramatic effects on the thermalconductivity and thermal shock resistance of matrices into which theyare incorporated.

Nanostructured fillers—in coated and uncoated form—and nanofilledcomposites are also expected to have significant value in biomedicalapplications for both humans and animals. For example, the small size ofnanostructured fillers may make them readily transportable through poresand capillaries. This suggests that the fillers may be of use indeveloping novel time-release drugs and methods of administration anddelivery of drugs, markers, and medical materials. A polymer coating canbe utilized either to make water-insoluble fillers into a form that iswater soluble, or to make water-soluble fillers into a form that iswater insoluble. A polymer coating on the filler may also be utilized asa means to time drug-release from a nanoparticle. A polymer coating mayfurther be used to enable selective filtering, transfer, capture, andremoval of species and molecules from blood into the nanoparticle.

A nanoparticulate filler for biomedical operations might be a carrier orsupport for a drug of interest, participate in the drug's functioning,or might even be the drug itself. Possible administration routes includeoral, topical, and injection routes. Nanoparticulates and nanocompositesmay also have utility as markers or as carriers for markers. Theirunique properties, including high mobility and unusual physicalproperties, make them particularly well-adapted for such tasks.

In some examples of biomedical functions, magnetic nanoparticles such asferrites may be utilized to carry drugs to a region of interest, wherethe particles may then be concentrated using a magnetic field.Photocatalytic nanoparticles can be utilized to carry drugs to region ofinterest and then photoactivated. Thermally sensitive nanoparticles cansimilarly be utilized to transport drugs or markers or species ofinterest and then thermally activated in the region of interest.Radioactive nanoparticulate fillers may have utility for chemotherapy.Nanoparticles suitably doped with genetic and culture material may beutilized in similar way to deliver therapy in target areas.Nanocomposites may be used to assist in concentrating the particle andthen providing the therapeutic action. To illustrate, magnetic andphotocatalytic nanoparticles may be formed into a composite,administered to a patient, concentrated in area of interest usingmagnetic field, and finally activated using photons in the concentratedarea. As markers, nanoparticulate fillers—coated or uncoated—may be usedfor diagnosis of medical conditions. For example, fillers may beconcentrated in a region of the body where they may be viewed bymagnetic resonance imaging or other techniques. In all of theseapplications, the possibility exists that nanoparticulates can bereleased into the body in a controlled fashion over a long time period,by implanting a nanocomposite material having a bioabsorbable matrix,which slowly dissolves in the body and releases its embedded filler.

As implants, nanostructured fillers and composites are expected to lowerwear rate and thereby enhance patient acceptance of surgical procedures.Nanostructured fillers may also be more desirable than micron-scalefillers, because the possibility exists that their domain size may bereduced to low enough levels that they can easily be removed by normalkidney action without the development of stones or other adverse sideeffects. While nanoparticulates may be removed naturally through kidneyand other organs, they may also be filtered or removed externallythrough membranes or otherwise removed directly from blood or tissue.Carrier nanoparticulates may be reactivated externally through membranesand reused; for example, nutrient carriers may be removed from thebloodstream, reloaded with more nutrients, and returned to carry thenutrients to tissue. The reverse process may also be feasible, whereincarriers accumulate waste products in the body, which are removedexternally, returning the carriers to the bloodstream to accumulate morewaste products.

Without limiting the scope of this invention, some exemplary methodswhich can be used to produce non-stoichiometric materials, are:

Method 1: Start with submicron powders, preferably nanopowders.Transform the powders into a non-stoichiometric form by one or more ofthe following techniques—heating in inert atmosphere, heating inoxidizing atmosphere, heating in reducing atmosphere, solventextraction, chemical reaction, electrochemical transformation,electromagnetic field treatment, ion beam treatment, electron beamtreatment, photonic treatment, rapid quench, plasma treatment, nuclearradiation, supercritical phase treatment, biological treatment, or acombination of one or more techniques. Utilize the non-stoichiometricmaterial so obtained. It may be desirable to sinter thenon-stoichiometric powders into a solid. It may further be desirable toreconvert the non-stoichiometric material to a stoichiometric form.

Method 2: Produce non-stoichiometric powders, preferably nanopowdersdirectly with techniques such as those taught in commonly assigned U.S.Pat. No. 5,788,738. Utilize the non-stoichiometric powders so obtained.For example, sinter and process them as appropriate. Finally, ifdesired, convert them to stoichiometric form.

Method 3: Mix nanoscale powders of a material and at least one of itscomponents in a desired ratio and heat the combination in an inert orother appropriate atmosphere to a temperature that completes the solidstate reaction. The material may comprise metallic, semimetallic, ornon-metallic components, or any combination thereof. It may be possibleto heat the materials in a reactive atmosphere to further control theratio desired among the components in the final product. Utilize thenon-stoichiometric substance so obtained.

Method 4: Add a dopant element with a valency different than one of theelectropositive constituents in the substance in which non-stoichiometryis to be engineered. Heat the mix to a temperature greater than thesolid state reaction temperature for a time that enables interminglingof the dopant element and the primary electropositive constituent. Theobjective in this procedure is to induce non-stoichiometry in a givensubstance because the distribution of secondary element introducesequivalent vacancies in the lattice of the substance.

Optimizing a Non-Stoichiometric Material

This invention enormously multiplies the number of novel substancealternatives available for producing devices and products. A preferredembodiment of this invention is to optimize the composition of thenon-stoichiometric substances for best performance. Such optimizationmay be accomplished by methods known in the art and by parallel searchapproaches such as the combinatorial search method taught by us in U.S.patent application Ser. No. 09/153,418 and by U.S. Pat. No. 5,776,359,both of which are incorporated by reference herein. One embodiment is toprepare samples of non-stoichiometric materials having differentcompositions and to evaluate the properties of the prepared samples. Thematerial with the best performance is selected as having the preferredcomposition. Another embodiment is to prepare samples ofnon-stoichiometric materials having different compositions, processthese samples into products, and evaluate each product's performance.Finally, the nanostructured non-stoichiometric material composition thatgives the best performing product is selected as the preferredcomposition. In yet another embodiment, a product is prepared from anon-stoichiometric substance and the non-stoichiometry varied in-situuntil the performance of the product is optimized with respect to thedesired specifications. Other methods may be utilized to select the bestcomposition. In all cases, it is important to consider all possibleperformance, environmental, and economic requirements of the productbefore a selection decision is made.

While the above approaches teach how to create and producenon-stoichiometric substances, useful products can be produced fromnanostructured non-stoichiometric substances by techniques and methodsalready known in the art. For example, if a porous body is desired, mixthe non-stoichiometric powders produced as above with an inert materialand reprocess the mixture. As appropriate, add a processing step whichwould remove the inert material using techniques such as dissolution,sublimation, evaporation, leaching, chemical reaction, or biologicalaction. This can lead to a porous body of nanostructured form.

If a given non-stoichiometric material is expensive to prepare, one canmix the non-stoichiometric powders produced as above with astoichiometric material and reprocess the mixture. This may help reducethe processing costs required in conversion from and to stoichiometricform.

One embodiment of this invention is to use non-stoichiometric forms ofmaterials as precursors for combinatorial discovery of materials andrelated technologies such as those disclosed in our commonly assignedU.S. patent application Ser. No. 09/153,418.

Another embodiment of this invention is to prepare devices fromnon-stoichiometric substances. Devices can be prepared using one of themanufacturing methods used currently in the art or a combinationthereof. Examples of processes which can be used at some stage includebut are not limited to pressing, extrusion, molding, screen printing,tape casting, spraying, doctor blading, sputtering, vapor deposition,epitaxy, electrochemical or electrophoretic deposition, thermophoreticdeposition, centrifugal forming, magnetic deposition, and stamping. Thenon-stoichiometric material in the device can be porous or dense, thinor thick, flat or curved, covered with a barrier or exposed. As alreadymentioned, with the motivation of improved performance, stableperformance, reduced costs, or a combination of these,non-stoichiometric materials may be converted partially or completelyinto a stoichiometric form or mixed with stoichiometric materials orboth after being processed into a device.

Another embodiment of this invention is to prepare a device fromstoichiometric materials and then convert the stoichiometric materialsinto a non-stoichiometric form. For example, a ferrite device can beprepared from stoichiometric magnetic materials which can then betransformed, partially or completely, into a non-stoichiometric form byheat treating the device in borane, ammonia, hydrogen, methane, orsilane to form a non-stoichiometric boride, nitride, oxide, hydride,carbide, silicide, or a combination thereof. In another example, asensor or battery device can be prepared from stoichiometricelectrochemical materials which can then be transformed, partially orcompletely, into a non-stoichiometric form by heat treating the devicein borane, ammonia, hydrogen, methane, or silane to form anon-stoichiometric boride, nitride, oxide, hydride, carbide, silicide,or a combination thereof. In a third example, a display device can beprepared from stoichiometric photonic materials which can then betransformed, partially or completely, into a non-stoichiometric form byheat treating the device in borane, ammonia, hydrogen, methane, orsilane to form a non-stoichiometric boride, nitride, oxide, hydride,carbide, silicide, or a combination thereof. In above examples inparticular, and this embodiment in general, the heat treatment can bereplaced by chemical methods, pressure, electrical methods, ionimplantation, or any other method or combination of methods. Inaddition, a substrate may be incorporated into the device. The substrateon which electrodes are formed can be flat or curved, flexible or rigid,inorganic or organic, thin or thick, porous or dense. The preferredsubstrates are those that provide the mechanical properties needed fordevice life greater than the anticipated device usage life.

In some embodiments of the presently claimed invention, it may bedesirable that the device be electroded. The electrode can be a wire orplate or coil, straight or curved, smooth or rough or wavy, thin orthick, solid or hollow, and flexible or non-flexible. For some devicedesigns, for example, bead/pellet type device designs, it is preferredthat the device is formed directly on the electrode wire or plate orcoil instead of on a substrate. It is important in all cases that theelectrode be conductive and stable at the usage temperatures. It ispreferred that the electrode composition does not react with thenon-stoichiometric substance or the environment during the manufactureor use of the device. The use of nanostructured forms ofnon-stoichiometric materials offers the benefit of sinteringtemperatures for devices which are lower than the sintering temperaturesachievable with coarser grained form. This may enable the use of lowercost electrode materials (e.g., copper or nickel instead of gold orplatinum). It is preferred that the non-stoichiometric form isnon-agglomerated and of a form that favors sintering. It is alsopreferred that the melting point of the electrode is higher than thehighest temperature to be used during the manufacture or use of thedevice. One of ordinary skill in the art will realize that other devicearchitectures can also be used in the presently claimed invention.Furthermore, non-stoichiometric form of electrodes can be utilized toimprove one or more performance parameters of the electrode in thedevice. Some examples of non-stoichiometric electrode substances areNiO_(1-x), NiO_(1-x)N, NiON_(1-x), Cu₂O_(1-x), and PdAgO_(1-x). Themethod described in this specification for preparing non-stoichiometricceramics may be utilized for preparing non-stoichiometric electrode aswell.

The device can be produced from various non-stoichiometric compositions,including ceramics, metals and alloys, polymers, and composites. Thenon-stoichiometric ceramics include but are not limited to binary,ternary, quaternary, or polyatomic forms of oxides, carbides, nitrides,borides, chalcogenides, halides, silicides, and phosphides. Theinvention also includes non-stoichiometric forms of ceramics, undopedand doped ceramics, and different phases of the same composition.

Metals and alloys such as those formed from a combination of two or moreof s group, p group, d group and f group elements may be utilized. Theinvention includes non-stoichiometric forms of alloys, undoped and dopedmetals and alloys, and different phases of the same composition.Polymers of non-stoichiometric formulations include but are not limitedto those with functional groups that enhance conductivity. Specificexamples include but are not limited to non-stoichiometric compositeswith stoichiometric polymers, defect conducting polymers, and ion-beamtreated polymers. One of ordinary skill in the art will realize thatother polymers, such as metal-filled polymers or conductingceramic-filled polymers, can also be used.

Device miniaturization is also a significant breakthrough that thepresently claimed invention offers through the use of nanostructurednon-stoichiometric materials. Existing precursors that are used toprepare devices are based on micron-sized powders. The mass of thedevice depends in part on the powder size because the device thicknesscannot be less than a few multiples of the precursor powder size. In amultilayer device, each layer cannot be less than a few multiples of theprecursor powder size. With nanostructured powders, the active elementsize and therefore its mass can be reduced significantly. For example,everything else remaining the same, the mass of a device can be reducedby a factor of 1000 if 10 nanometer powders are used instead of 10micron powders. This method of reducing mass and size is relevant todevices in the electronics, electrical, magnetic, telecommunication,biomedical, photonic, sensors, electrochemical, instruments, structural,entertainment, education, display, marker, packaging, thermal, acoustic,and other industries. The presently claimed invention teaches thatnanostructured non-stoichiometric powders are preferred to reduce themass and size of a device.

EXAMPLES Example 1 Indium Tin Oxide Fillers in PMMA

A stoichiometric (90 wt % ln203 in SnO₂) indium tin oxide (ITO)nanopowder was produced using the methods of copending patentapplication Ser. No. 09/046,465. 50 g of indium shot was placed in 300ml of glacial acetic acid and 10 ml of nitric acid. The combination, ina 1000 ml Erlenmeyer flask, was heated to reflux while stirring for 24hours. At this point, 50 ml of HNO₃ was added, and the mixture washeated and stirred overnight. The solution so produced was clear, withall of the indium metal dissolved into the solution, and had a totalfinal volume of 318 ml. An equal volume (318 mL) of 1-octanol was addedto the solution along with 600 mL ethyl alcohol in a 1000 mL HDPEbottle, and the resulting mixture was vigorously shaken. 11.25 ml oftetrabutyltin was then stirred into the solution to produce a clearindium/tin emulsion. When the resulting emulsion was burned in air, itproduced a brilliant violet flame. A yellow nanopowder residue wascollected from the flamed emulsion. The nanopowder surface area was 13.5m²/gm, and x-ray diffractometer mean grain size was 60 nm.

FIG. 2 shows the measured X-ray diffraction (XRD) spectrum for thepowder, and FIG. 3 shows a scanning electron microscope (SEM image ofthe powder. These data show that the powder was of nanometer scale.

The nanostructured powder was then mixed with poly(methyl methacrylate)(PMMA) in a ratio of 20 vol % powder to 80 vol % PMMA. The powder andthe polymer were mixed using a mortar and pestle, and then separatedinto three parts, each of which was pressed into a pellet. The pelletswere pressed by using a Carver hydraulic press, pressing the mixtureinto a ¼ inch diameter die using a 1500 pound load for one minute.

After removal from the die, the physical dimensions of the pellets weremeasured, and the pellets were electroded with silver screen printingpaste (Electro Sciences Laboratory 9912-F).

Pellet resistances were measured at 1 volt using a Megohmmeter/IR tester1865 from QuadTech with a QuadTech component test fixture. The volumeresistivity was calculated for each pellet using the standard relation,$\begin{matrix}{\rho = {R\left( \frac{A}{t} \right)}} & (1)\end{matrix}$

where ρ represents volume resistivity in ohm-cm, R represents themeasured resistance in ohms, A represents the area of the electrodedsurface of the pellet in cm², and t represents the thickness of thepellet in cm. The average volume resistivity of the stoichiometric ITOcomposite pellets was found to be 1.75×10⁴ ohm-cm.

Another quantity of ITO nanopowder was produced as described above, andwas reduced by passing 2 SCFM of forming gas (5% hydrogen in nitrogen)over the powder while ramping temperature from 25° C. to 250° C. at 5°C./min. The powder was held at 250° C. for 3 hours, and then cooled backto room temperature. The XRD spectrum of the resulting powder indicatedthat the stoichiometry of the reduced powder was In₁₈SnO_(29-x), with xgreater than 0 and less than 29.

The reduced ITO nanopowder was combined with PMMA in a 20:80 volumeratio and formed into pellets as described above. The pellets wereelectroded as described, and their resistivity was measured. The averageresistivity for the reduced ITO composite pellets was found to be1.09×10⁴ ohm-cm.

For comparison, micron scale ITO was purchased from Alfa Aesar (catalognumber 36348), and was formed into pellets with PMMA and electroded asdescribed above. Again, the volume fraction of ITO was 20%. The averagemeasured resistivity of the micron scale ITO composite pellets was foundto be 8.26×10⁸ ohm-cm, representing a difference of more than fourorders of magnitude from the nanoscale composite pellets. It was thusestablished that composites incorporating nanoscale fillers can haveunique properties not achievable by prior art techniques.

Example 2 Hafnium Carbide Fillers in PMMA

Composite pellets were produced as described in Example 1, by mixingfiller and polymer with a mortar and pestle and pressing in a hydraulicpress. Pellets were produced containing either nanoscale or micron scalepowder at three loadings: 20 vol % powder, 50 vol % powder, and 80 vol %powder. The pellets were electroded as described above, and theirresistivities were measured. (Because of the high resistances at the 20%loading, these pellets' resistivities were measured at 100V. The otherpellets were measured at IV, as described in Example 1).

Results of these resistivity measurements are summarized in Table 1. Ascan be seen, the resistivity of the pellets differed substantiallybetween the nanoscale and micron scale powders. The compositesincorporating nanoscale powder had a somewhat decreased resistivitycompared to the micron scale powder at 20% loading, but had adramatically increased resistivity compared to the micron scale powderat 50% and 80% loading. TABLE 1 Resistivity of nanoscale Resistivity ofmicron scale powder composite powder composite Volume % filler (ohm-cm)(ohm-cm) 20  5.54 × 10¹²  7.33 × 10¹³ 50 7.54 × 10⁹ 2.13 × 10⁴ 80 3.44 ×10⁹ 1.14 × 10⁴

Example 3 Copper Fillers in PMA and PVA

Nanoscale copper powders were produced as described in U.S. patentapplications Ser. Nos. 08/706,819 and 08/707,341. The nanopower surfacearea was 28.1 m2/gm, and mean grain size was 22 nm. Micron scale copperpowder was purchased from Aldrich (catalog number 32645-3) forcomparison.

The nanoscale and micron scale copper powders were each mixed at aloading of 20 vol % copper to 80 vol % PMMA and formed into pellets asdescribed above. In addition, pellets having a loading of 15 vol %copper in poly(vinyl alcohol) (PVA) were produced by the same method.The pellets were electroded and resistivities measured at 1 volt asdescribed in Example 1. Results are shown in Table 2. TABLE 2 VolumeResistivity Additive Polymer Volume % filler (ohm-cm) nanoscale copperPMMA 20 5.68 × 10¹⁰ nanoscale copper PVA 15 4.59 × 10⁵  micron scalecopper PMMA 20 4.19 × 10¹²

It can be seen from Table 2 that the resistivity of the nanoscale copperpowder/PMMA composite was substantially reduced compared to the micronscale copper powder/PMMA composite at the same loading, and that theresistivity of the nanoscale copper powder/PVA composite was lower stillby five orders of magnitude.

Example 4 Preparation of Polymer-Coated Nanostructured Filler

The stoichiometric (90 wt % In₂O₃ in SnO₂) indium tin oxide (ITO)nanopowder of Example 1 was coated with a polymer as follows.

200 milligrams of ITO nanopowders with specific surface area of 53 m²/gmwere added to 200 ml of demineralized water. The pH of the suspensionwas adjusted to 8.45 using ammonium hydroxide. In another container, 200milligrams of poly(methyl methacrylate) (PMMA) was dissolved in 200 mlof ethanol. The PMMA solution was warmed to 100° C. while being stirred.The ITO suspension was added to the PMMA solution and the stirring andtemperature of 100° C. was maintained till the solution reduced to avolume of 200 ml. The solution was then cooled to room temperature to avery homogenous solution with very light clear-milky color. The opticalclarity confirmed that the powders are still nanostructured. The powderwas dried in oven at 120° C. and its weight was measured to be 400milligrams. The increase in weight, uniformity of morphology and theoptical clarity confirmed that the nanopowders were coated with PMMApolymer.

The electrochemical properties of polymer coated nanopowders weredifferent than the as-produced nanopowders. The as-produced nanopowderwhen suspended in demineralized water yielded a pH of 3.4, while thepolymer coated nanopowders had a pH of 7.51.

Example 5 Preparation of Electrical Device Using Nanostructured Fillers

A complex oxide nanoscale filler having the following composition wasprepared: Bi₂O₃ (48.8 wt %), NiO (24.4 wt %), CoO (12.2 wt %), Cr₂O₃(2.4 wt %), MnO (12.2 wt %), and Al₂O₃ (<0.02 wt %). The complex oxidefiller was prepared from the corresponding nitrates of the same cation.The nitrates of each constituent were added to 200 mL of deionized waterwhile constantly stirring. Hydroxides were precipitated with theaddition of 50 drops of 28-30% NH₄OH. The solution was filtered in alarge buchner funnel and washed with deionized water and then with ethylalcohol. The powder was dried in an oven at 80° C. for 30 minutes. Thedried powder was ground using a mortar and pestle. A heat treatmentschedule consisting of a 15° C./min ramp to 350° C. with a 30 minutedwell was used to calcine the ground powder.

The nanofiller was then incorporated at a loading of 4% into a zincoxide ceramic matrix. The composite was prepared by mechanically mixingthe doped oxide nanofiller powder with zinc oxide powder, incorporatingthe mixture into a slurry, and screen printing the slurry (furtherdescribed below). For comparison, devices were made using both ananoscale matrix powder produced by the methods of copending andcommonly assigned U.S. application Ser. No. 08/706,819, and using amicron scale matrix powder purchased from Chemcorp. The fillers and thematrix powders were mixed mechanically using a mortar and pestle.

Using the filler-added micron scale powder, a paste was prepared bymixing 4.0 g of powder with 2.1 g of a commercial screen printingvehicle purchased from Electro Science Laboratories (ESL vehicle 400).The doped nanoscale powder paste was made using 3.5 g powder and 3.0 gESL vehicle 400. Each paste was mixed using a glass stir rod.Silver-palladium was used as a conducting electrode material. A screenwith a rectangular array pattern was used to print each paste on analumina substrate. First a layer of silver-palladium powder (the lowerelectrode) was screen printed on the substrate and dried on a hot plate.Then the ceramic filled powder was deposited, also by screen printing.Four print-dry cycles were used to minimize the possibility of pinholedefects in the varistor. Finally, the upper electrode was deposited.

The electrode/composite/electrode varistor was formed as threediagonally offset overlapping squares, as illustrated in FIG. 4. Theeffective nanostructured-filler based composite area in the device dueto the offset of the electrodes was 0.036 in² (0.2315 cm²). The greenthick films were co-fired at 900° C. for 60 minutes. The screen printedspecimen is shown in FIG. 4, where light squares 10 represent thesilver-palladium electrodes, and dark square 12 represents the compositelayer.

Silver leads were attached to the electrodes using silver epoxy. Theepoxy was cured by heating at a 50° C./min ramp rate to 600° C. and thencooling to room temperature at a rate of 50° C./min. The TestPointcomputer software, in conjunction with a Keithley® current source, wasused to obtain a current-voltage curve for each of the varistors.Testpoint and Keithley are trademarks or registered trademark ofKeithley Scientific Instruments, Inc.

The electrode/micron scale matrix composite/electrode based varistordevice had a total thickness of 29-33 microns and a composite layerthickness of 19 microns. The electrode/nanoscale matrixcomposite/electrode based varistor device had a total thickness of 28-29microns and a composite layer thickness of 16 microns. Examination ofcurrent-voltage response curves for both varistors showed that thenanostructured matrix varistor had an inflection voltage of about 2volts, while the inflection voltage of the micron scale matrix varistorhad an inflection voltage of about 36 volts. Fitting the current-voltageresponse curves to the standard varistor power-law equationI=nV^(a)   (2)yielded values of voltage parameter a of 2.4 for the micron-scale matrixdevice, and 37.7 for the nanoscale matrix device. Thus, the nonlinearityof the device was shown to increase dramatically when the nanoscalematrix powder was employed.

Example 6 Thermal Battery Electrode using a Nanostructured Filler

Thermal batteries are primary batteries ideally suited for militaryordinance, projectiles, mines, decoys, torpedoes, and space explorationsystems, where they are used as highly reliable energy sources with highpower density and extremely long shelf life. Thermal batteries havepreviously been manufactured using techniques that place inherent limitson the minimum thickness obtainable while ensuring adequate mechanicalstrength. This in turn has slowed miniaturization efforts and haslimited achievable power densities, activation characteristics, safety,and other important performance characteristics. Nanocomposites helpovercome this problem, as shown in the following example.

Three grams of raw FeS₂ powder was mixed and milled with a group of hardsteel balls in a high energy ball mill for 30 hours. The grain size ofproduced powder was 25 nm. BET analysis showed the surface area of thenanopowder to be 6.61 m²/gm. The TEM images confirmed that the ballmilled FeS₂ powder consists of the fine particles with the round shape,similar thickness and homogenous size. The cathode comprised FeS₂nanopowders (68%), eutectic LiCl—KCl (30%) and SiO₂ (2%) (from AldrichChemical with 99% purity). The eutectic salts enhanced the diffusion ofLi ions and acted as a binder. Adding silicon oxide particles wasexpected to immobilize the LiCl—KCl salt during melting. For comparison,the cathode pellets were prepared from nanostructured and micron scaleFeS₂ powders separately.

To improve electrochemical efficiencies and increase the melting pointof anode, we chose micron scale Li 44%-Si 56% alloy with 99.5% purity(acquired from Cyprus Foote Mineral) as the anode material in this work.A eutectic salt, LiCl 45%-KCl 55% (from Aldrich Chemical with 99%purity), was selected as electrolyte. The salt was dried at 90° C. andfused at 500° C. To strengthen the pellets and prevent flowing out ofelectrolyte when it melted, 35% MgO (Aldrich Chemical, 99% purity)powder was added and mixed homogeneously with the eutectic salt powder.

The pellets of anode electrodes were prepared by a cold press process. Ahard steel die with a 20 mm internal diameter was used to make the thindisk pellets. 0.314 grams of Li 44%-Si 56% alloy powder (with 76-422mesh particle size) was pressed under 6000 psi static pressure to form apellet. The thickness and density of the pellets so obtained wasdetermined to be 0.84 mm and 1.25 g/cm², respectively. Electrolytepellets were produced using 0.55 grams of blended electrolyte powderunder 4000 psi static pressure. The thickness and density of the pelletsobtained were 0.84 mm and 2.08 g/cm² respectively. The cathode pelletwas prepared using 0.91 grams of mixed micron scale FeS₂ —LiCl—KCI—SiO₂powder pressed under 4000 psi static pressure. The thickness and densityof the pellets obtained were 0.86 mm and 3.37 g/cm², respectively.

A computerized SOLARTRON® 1287 electrochemical interface and a 1260Gain/Phase Analyzer were employed to provide constant current and tomonitor variation in potential between anode and cathode of cells duringthe discharging. “Solartron” is a registered trademark of the SolartronElectronic Group, Ltd. The cutoff potential of discharge was set at 0.8volt. The thermal battery with the nanocomposite cathode provided 1 Aconstant current for 246 seconds, until the potential fell to 0.8 volt.It was observed that the power density of the nanostructured single cellthermal battery was 100% higher than that achievable with micron sizedmaterials. Thus, nanoscale fillers can help enhance the electrochemicalperformance of such a device.

Example 7 A Magnetic Device Using Nanostructured Ferrite Fillers

Ferrite inductors were prepared using nanostructured and micron-scalepowders follows. One-tenth of a mole (27.3 grams) of iron chloridehexahydrate (FeCl₃ -6H₂ as O) was dissolved in 500 ml of distilled wateralong with 0.025 moles (3.24 grams) of nickel chloride (NiCl₂) and 0.025moles (3.41 grams) of zinc chloride (ZnCl₂). In another large beaker, 25grams of NaOH was dissolved in 500 ml of distilled water. While stirringthe NaOH solution rapidly, the metal chloride solution was slowly added,forming a precipitate instantaneously. After 1 minute of stirring, theprecipitate solution was vacuum filtered while frequently rinsing withdistilled water. After the precipitate had dried enough to cake andcrack, it was transferred to a glass dish and allowed to dry for 1 hourin an 80° C. drying oven. At this point, the precipitate was ground witha mortar and pestle and calcined in air at 400° C. for 1 hour to removeany remaining moisture and organics.

BET analysis of the produced powder yielded a surface area of 112 m²/g,confirming the presence of nanometer-sized individual particles with anestimated BET particle size of 11 nm. XRD analyses of all nanoscalepowders showed the formation of a single (Ni, Zn)Fe₂O₄ ferrite phasewith peak shapes characteristic of nanoscale powders. XRD peakbroadening calculations reported an average crystallite size of 20 nm ofthe thermally quenched powders and 8 nm for the chemically derivedpowders. SEM-EDX analyses of sintered nanopowder pellets showed anaverage composition of 14.8% NiO, 15.8% ZnO, and 69.4% Fe₂O₃, whichcorresponded to the targeted stoichiometric composition of theNi_(0.5)Zn_(0.5)Fe₂O₄.

Nanoscale ferrite filler powders were uniaxially pressed at 5000 poundsin a quarter-inch diameter die set into green pellets. The powders weremixed with 2 weight percent Duramax® binder for improved sinterability.The amount of powder used for pressing varied from 1.5 to 1.7 grams,typically resulting in cylinders having a post-sintered height ofapproximately 1.5 cm. To avoid cracking and other thermal stresseffects, a multi-level heating profile was employed. The pellets werefired at a rate of 5° C./min to 300° C., 10° C./min to 600° C., and 20°C./min to the final sintering temperature, where it was held for fourhours. Pellets were cooled from the sintering temperature at a rate of10° C./min to ensure the sintering temperature ranged from 900° C. to1300° C., but was typically greater than 1200° C. to ensure anacceptable density. Sintered pellets were then wound with 25 turns of 36gauge enamel coated wire, the wire ends were stripped, and the completedsolenoids where used for electrical characterization. An air coil wasprepared for the purpose of calculating magnetic properties. This coilwas created by winding 25 turns of the enamel coated wire around the dieplunger used previously. This coil was taped with masking tape, slid offthe plunger slowly to maintain shape and characteristics, and wascharacterized along with the ferrite solenoids.

Inductance characterization was performed with a Hewlett-Packard 429A RFImpedance/Materials Analyzer. Impedance, parallel inductance, q factor,and impedance resistance were measured over a logarithmic frequencysweep starting at 1 MHz and ending at 1.8 GHz. Values for permeability(μ) and loss factor (LF) were calculated from inductance (L), air coilinductance (L_(o)), and impedance resistance (R) using the followingequations: $\begin{matrix}{\mu = \frac{L}{L_{0}}} & (3) \\{{LF} = \frac{L_{0}R}{\omega\quad L^{2}}} & (4)\end{matrix}$

Resistivity measurements were made with a Keithley® 2400 SourceMeterusing a four-wire probe attachment and TestPoint™ data acquisitionsoftware. Voltage was ramped from 0.1 to 20 volts while simultaneouslymeasuring current. The results were plotted as field (voltage divided bypellet thickness) versus current density (current divided by electrodecross sectional area). The slope of this graph gives materialresistivity (ρ).

Table 3 summarizes electrical properties of inductors prepared frommicron-sized powder or from nanopowder. In most cases there is anadvantage to using nanoscale precursor powder instead of micron-sizedpowder. It is important to keep in mind that all measurements were takenfrom cylindrical devices, which have inherently inefficient magneticproperties. Solenoids of this shape were used in this study because ofthe ease of production and excellent reproducibility. All measuredproperties would be expected to improve with the use of higher magneticefficiency shapes such as cores or toroids, or by improving the aspectratio (length divided by diameter) of the cylindrical samples. TABLE 3Loss Factor @ 1 MHz Critical Frequency Micron Nano Micron Nano Average0.0032 0.0025 Average 68.9 MHz 78.3 MHz Q Factor @ 1 MHz ResistivityMicron Nano Micron Nano Average 37.2 52.2 Average 0.84 MΩ 33.1 MΩ

The inductors made from ferrite nanopowders exhibited significantlyhigher Q-factor, critical resonance frequency, and resistivity. Theyalso exhibited more than 20% lower loss factor as is desired incommercial applications.

Example 8 Tungsten Oxide

Ammonium meta-tungstate (55 g) was placed in a 500 ml beaker withethylene glycol (100 mL). This mixture was stirred to form a clearsolution. While stirring, 500 mL of Igepal®. 520-CO and 500 mL ofnaphtha were added to the solution, yielding a clear emulsiontungstate/glycol solution (polar phase) in naptha (non-polar phase). TheIgepal® 520-CO served as an emulsifying agent. Igepal is a registeredtrademark of Rhone-Poulenc Surfactants and Specialties, L.P.

Combustion of the emulsion produced an incandescent flame. A yellowpowder, characteristic of tungsten oxide, was visible depositing withinthe combustion chamber. TEM and SEM observations indicated that thepowder consisted of particles with both equiaxed (<100 nm) and acicularmorphologies (e.g., 10×100 nm), and that the powder comprised solelysub-micron particles. These particle sizes are corroborated by X-raydiffraction data, suggesting crystallite sizes ranging from 14 to 33 nmfor the primary peaks of the hexagonal WO₃ powder, a mean minimum domainsize of about 25 nm and a standard deviation of about 7 nm. The specificsurface area as measured by Brunauer, Emmett, and Teller analysis(described in more detail in Brunauer, et al., J. Am. Chem. Soc.,60:309, 1938, and hereinafter referred to as BET) was 31.5 m²/g, givinga 30 nm equivalent spherical diameter. The experiment also produced WO₃nanowhiskers and nanorods with aspect ratios ranging from 5 to 15.

Example 9 Tungsten-Doped Tin Oxide

Ammonium meta-tungstate (7.95 g) was placed in a 500 ml beaker withethylene glycol (10 mL). This mixture was stirred to form a clearsolution. While stirring, 200 mL of Igepal® 520-CO and 200 mL of naphthawere added to the solution, yielding a clear emulsion tungstate/glycolsolution (polar phase) in naptha (non-polar phase). The Igepal® 520-COserved as an emulsifying agent. Tetrabutyl tin (98.37 g) was added tothe solution and naphtha was added to make a 700 mL volume.

Flaming of the emulsion produced an incandescent flame. A steel-bluepowder was collected and characterized. The powder consists of facetedand equiaxed particles ranging from 10 to 75 nm showing solelysub-micron powder. Both nanowhiskers and equiaxed particles are present.The aspect ratios of the nanowhiskers were in the range of 3-20.Crystallite sizes as measured by X-ray diffraction range from 20 to 30nm for the primary peaks of the SnO₂ powder, and there are no apparentsecondary phases attributable to tungsten. The mean minimum domain sizeas calculated from the XRD data was about 27 nm and the standarddeviation was estimated to be about 10 nm. The presence of tungsten wasconfirmed by X-Ray Electron Diffraction Spectroscopy (XEDS) both in theSEM and the TEM. The BET specific surface area was 35 m²/g, giving anequivalent spherical diameter of about 20-30 nm.

Example 10 Copper Doped Nickel Zinc Ferrite

Commercially purchased metal-carboxylate emulsions (OMG Americas,Westlake, Ohio) were combined to form a clear emulsified solution thatwould yield the appropriate metal ratios to synthesize 300 g of theoxide. Flaming of the emulsion produced a brilliant incandescent flame.A chocolate-brown powder was collected and characterized. XRD datayielded crystallite sizes in the range of 20-40 nm, and indicated thatthe powder was a phase-pure spinel ferrite. The presence of allconstituent elements was confirmed by XEDS in the SEM. The mean particlesize of the powder was about 29 nm and the standard deviation was about8 nm.

Example 11 Zinc

Commercially available zinc powder (−325 mesh) was used as the precursorto produce nanosize zinc powder. Feed zinc powder was fed into thethermal reactor suspended in an argon stream (argon was used as theplasma gas; the total argon flow rate was 2.5 ft³/min). The reactor wasinductively heated with 16 kW of RF plasma to over 5,000K in the plasmazone and about 3,000K in the extended reactor zone adjacent theconverging portion of the nozzle. The vaporized stream was quenchedthrough the converging-diverging nozzle. The preferred pressure dropacross the nozzle was 250 Torr, but useful results were obtained atdifferent pressure drops, ranging from 100 to 550 Torr. After undergoinga pressure drop of 100 to 550 Torr through the converging-divergingnozzle, the powder produced was separated from the gas by means of acooled copper-coil-based impact filter followed by a screen filter. Thenanosize powder produced by the invention were in the 5-25 nanometerrange. The size distribution was narrow, with a mean size ofapproximately 15 nm and a standard deviation of about 7.5 nm.

Example 12 Iron-Titanium Intermetallic

2-5 micron powders of iron and 10-25 micron powders of titanium weremixed in 1:1 molar ratio and fed into the thermal reactor suspended inan argon stream (total gas flow rate, including plasma gas, was 2.75 ft³/min). The reactor was inductively heated with 18 kW of RF plasma toover 5,000K in the plasma zone and above 3,000K in the extended reactorzone adjacent the converging portion of the nozzle. The vaporized streamwas quenched through the converging-diverging nozzle. The preferredpressure drop across the nozzle was 250 Torr, but useful results wereobtained at different pressure drops, ranging from 100 to 550 Torr.After undergoing a pressure drop of 100 to 550 Torr through theconverging-diverging nozzle, the powder produced was separated from thegas by means of a cooled copper-coil-based impact filter followed by ascreen filter. The nanopowders produced by the invention were in the10-45 nanometer range. The size distribution was narrow, with a meansize of approximately 32 nm and a standard deviation of about 13.3 nm.

Example 13 Tungsten Oxide

Commercially available tungsten oxide powder (−325 mesh size) was usedas the precursor to produce nanosize WO₃. The tungsten oxide powder wassuspended in a mixture of argon and oxygen as the feed stream (flowrates were 2.25 ft³/min for argon and 0.25 ft.sup.3 /min for oxygen).The reactor was inductively heated with 18 kW of RF plasma to over5,000K in the plasma zone and about 3,000K in the extended reactor zoneadjacent the converging portion of the nozzle. The vaporized stream wasquenched through the converging-diverging nozzle. The preferred pressuredrop across the nozzle was 250 Torr, but useful results were obtained atdifferent pressure drops, ranging from 100 to 550 Torr. After undergoinga pressure drop of 100 to 550 Torr through the converging-divergingnozzle, the powder produced was separated from the gas by means of acooled copper-coil-based impact filter followed by a screen filter. Thepowder produced by the invention were in the 10-25 nanometer range. Thesize distribution was narrow, with a mean size of about 16.1 nm and astandard deviation of about 6.3 nm.

Example 14 Cerium Oxide

Commercially available cerium oxide powder (5-10 micron size) was usedas the precursor to produce nanosize CeO₂. The cerium oxide powder wassuspended in a mixture of argon and oxygen as the feed stream (at totalrates of 2.25 ft³ /min for argon and 0.25 ft³ /min for oxygen). Thereactor was inductively heated with 18 kW of RF plasma to over 5,000K inthe plasma zone and about 3,000K in the extended reactor zone adjacentthe converging portion of the nozzle. The vaporized stream was quenchedthrough the converging-diverging nozzle. The preferred pressure dropacross the nozzle was 250 Torr, but useful results were obtained atdifferent pressure drops, ranging from 100 to 650 Torr. The powderproduced was separated from the gas by means of a cooledcopper-coil-based impact filter followed by a screen filter. The powderproduced by the invention was in the 5-25 nanometer range. The sizedistribution was narrow, with a mean size of about 18.6 nm and astandard deviation of about 5.8 nm.

Example 15 Silicon Carbide

Commercially available silicon carbide powder (−325 mesh size) was usedas the precursor to produce nanosize SiC. The powder was suspended inargon as the feed stream (total argon flow rate of 2.5 ft³/min). Thereactor was inductively heated with 18 kW of RF plasma to over 5,000K inthe plasma zone and about 3,000K in the extended reactor zone adjacentthe converging portion of the nozzle. The vaporized stream was quenchedthrough the converging-diverging nozzle. The preferred pressure dropacross the nozzle was 250 Torr, but useful results were obtained atdifferent pressure drops, ranging from 100 to 550 Torr. The powderproduced was separated from the gas by means of a cooledcopper-coil-based impact filter followed by a screen filter. The SiCpowder produced by the invention were in the 10-40 nanometer range. Thesize distribution was narrow, with a mean size of approximately 28 nmand a standard deviation of about 8.4 nm.

Example 16 Molybdenum Nitride

Commercially available molybdenum oxide (MoO₃) powder (−325 mesh size)was used as the precursor to produce nanosize Mo₂N. Argon was used asthe plasma gas at a feed rate of 2.5 ft³/min. A mixture of ammonia andhydrogen was used as the reactant gases (NH₃ at 0.1 ft³/min; H₂ at 0.1ft³/min). The reactor was inductively heated with 18 kW of RF plasma toover 5,000K in the plasma zone and about 3,000K in the extended reactorzone adjacent the converging portion of the nozzle. The vaporized streamwas quenched through the converging-diverging nozzle. The preferredpressure drop across the nozzle was 250 Torr, but useful results wereobtained at different pressure drops, ranging from 100 to 550 Torr. Thepowder produced was separated from the gas by means of a cooledcopper-coil-based impact filter followed by a screen filter. The Mo₂Npowder produced by the invention was in the 5-30 nanometer range. Thesize distribution was narrow, with a mean size of about 14 nm and astandard deviation of about 4.6 nm.

Example 17 Nickel Boride

10-50 micron powder of nickel boride were fed into the thermal reactorwith argon (fed at a total rate, including plasma gas, of 2.75 ft³/min).Once again, the reactor was inductively heated with 18 kW of RF plasmato over 5,000K in the plasma zone and about 3,000K in the extendedreactor zone adjacent the converging portion of the nozzle. Thevaporized stream was quenched through the converging-diverging nozzle.The preferred pressure drop across the nozzle was 250 Torr, but usefulresults were obtained at different pressure drops, ranging from 100 to550 Torr. The powder produced was separated from the gas by means of acooled copper-coil-based impact filter followed by a screen filter. TheNi₃B powder produced by the invention was in the 10 to 30 nanometerrange. The size distribution was narrow, with a mean size of about 12.8nm and a standard deviation of about 4.2 nm.

Example 18 Processing of Materials

Densification of powders, or sintering, is essentially a process ofremoving the pores between the starting particles, combined with growthand strong bonding between adjacent particles. The driving force fordensification is the free-energy change, or more specifically, thedecrease in surface area and lowering of the free energy.

Among the processing variables that may affect the densificationprocess, the particle size of the starting powder is one of the mostimportant variables. In solid-state processes, assuming that the mattertransport is controlled by lattice diffusion, the volume change of thematerial with respect to time during sintering can be related toprocessing variables as follows:$\frac{\_ V}{V_{o}} = \left\lbrack {3\left( \frac{20\gamma\quad a^{3}{D{^\circ}}}{\sqrt{2}{kT}} \right)r^{- 1.2}t^{0.4}} \right\rbrack$

In this equation, V_(o) and _V are the initial volume and volume changeof the target during densification, respectively; T is the sinteringtemperature; t the sintering time; k the Boltzman constant, D^(o) theself-diffusivity, γ the surface energy of the particle, a³ the atomicvolume of the diffusing vacancy, and r the radius of the particle of thestarting powder.

As we can see from the above equation, the sintering time needed toachieve a specific degree of densification is proportional to the cubeof the particle size of the starting powder. Given the same sinteringtemperature and starting material, the densification rate can beincreased drastically by using 100 nm sized powders instead of 10 nmsized powders. Alternatively, to obtain the same densification or toprevent the decomposition of a fragile material at high temperatures,sintering can be conducted at lower temperature with nanostructuredpowders. Thus, nano-sized materials can also significantly decrease thesintering temperatures currently used for micrometer-sized powders. Froma commercial viewpoint, the energy savings from lower processingtemperatures and the reduction of processing times can be substantial.

Another beneficial effect of using nano-sized powders is that, becauseof high surface area and surface diffusivity, nano-sized composites maybe sintered without impurity inducing sintering aids, resulting in morereliable sintered products which exhibit enhanced service temperaturesand high temperature strength. Other anticipated benefits describedbelow include commercially attractive processing times and temperatures,lowered inventory costs, use of lower cost precursors, and the abilityto sinter devices at temperatures that prevent undesirable secondaryreactions or transformations during device fabrication. While thisapplication prefers the use of nanopowders, the teachings herein can beapplied to submicron and larger non-stoichiometric powders.

For example, put the non-stoichiometric material in a die and press thematerial to green densities of 40% or higher. Alternatively, useinjection molding, CIP, HIP, electrophoretic, magnetophoretic, coatings,gel casting, dip coating, precipitation, thick film forming, molding,screen printing, extrusion, and any of techniques known in the art toform a body from the non-stoichiometric nanopowder prepared. Next,sinter the prepared body using a temperature, time, atmosphere, andelectromagnetic field sufficient to reach desired density. If desired,the sintering step may be followed by machining or processing thedensified form as appropriate. Finally, transform the densified andprocessed non-stoichiometric structure to stoichiometric form.

The motivation of this approach is explained above and further includesthe following: The stoichiometric form of M_(n/p)Z_(1-x) may be given byx=0 (i.e. M_(n/p)Z) the lower bound case of the inequality 0<x<1. Whenx=1, we get the upper inequality bound and this represents the pureelement M. It is known to those skilled in the art that the sinteringcharacteristics of M and M_(n/p)Z are very different. Often, M is easierto consolidate and sinter than M_(n/p)Z. Thus, the use of M_(n/p)Z_(1-x)is anticipated to offer performance intermediate to M and M_(n/p)Z. Froma thermodynamic point of view, the unusual interfacial free energies ofnon-stoichiometric forms can allow the use of more commerciallyattractive sintering conditions (i.e. temperature, time, field, andatmosphere) to produce the product of interest. Also, by utilizing thenon-stoichiometric form M_(n/p)Z_(1-x), the unusual properties of thenon-stoichiometric form can be beneficially applied to produce usefulobjects from powders or porous bodies.

For example, in the case of Ti and TiO₂, the sintering temperatures formetal and metal oxide are very different. Metals are easier to sinterand process metals than ceramics. It is expected that the sinteringcharacteristics of a material form intermediate to the two extremes (x=0and x=1) would also be different, in a linear or non-linear manner, thanthe two extremes. It is anticipated that non-stoichiometric forms oftitania will be more reactive, that vacancies will assist pore volumereduction, and that these will reduce the time and temperature needed todensify a structure.

Yet another example would be to use non-stoichiometric forms of doped orundoped superconductors, ferrites, carbides, borides, nitrides, alloys,and oxides, such as NiO, BaTiO₃, ZrO₂, and hafnia. The melting point ofa metal is often less than that of the corresponding ceramic form. Theuse of non-stoichiometric compositions can assist in achieving denseforms at lower temperatures or reduce the time needed to densify amaterial at a given temperature.

In some applications, the unusual properties of non-stoichiometricmaterial may suggest that the device be used in a non-stoichiometricform. However, such devices may change their performance over time orhave other disadvantages. Such problems can be addressed through the useof protective coatings, secondary phases, and stabilizers.

Dense sputtering targets of various compositions can also be preparedusing the above method. These targets can then be used to prepare thinfilms for electronic, information storage, optics, and various otherproducts.

The motivation to use these teachings includes commercially attractiveprocessing times and temperatures, lowered inventory costs, use of lowercost precursors, and the ability to sinter devices at temperatures thatprevent undesirable secondary reactions or transformations during devicefabrication.

Example 19 Catalysis

Nanopowders comprising 75% by weight indium tin oxide (ITO) (mean grainsize: 12.9 nm, 60.9 m²/gm) and 25% by weight alumina (mean grain size:4.6 nm, 56 m²/gm) were mixed and pressed into pellets weighingapproximately 200 mg. The pellet was reduced in a 100 ml/min 5% H-95% Arstream at 300° C. for 10 minutes. The yellow pellet became a bluishgreen color. The pellet was exposed to 12% methanol vapor in air (100ml/min) at about 250° C. and the product gases analyzed using Varian3600 Gas Chromatograph. The gas composition analysis indicated that theproduct gases contained 3400 ppm of hydrogen, suggesting catalyticactivity from the non-stoichiometric blue green pellet. This is incontrast with the observation that the pellet showed no catalyticactivity, every thing else remaining same, when the color was yellow.The blue green pellet was replaced with a platinum wire and thetemperature raised to about 250° C. No catalytic activity was detectablefor the platinum wire at this temperature. These observations suggestthat the non-stoichiometric indium tin oxide has unique and surprisingcatalytic properties when contrasted with stoichiometric indium tinoxide.

Example 20 Photonics and Optics

Stoichiometric ITO (yellow, 30 nm mean grain size) was produced via themethod of commonly assigned U.S. Pat. No. 5,788,738 by feeding ITO inair. Non-stoichiometric ITO (bluish black, 30 nm mean grain size) wasproduced using the method of commonly assigned U.S. Pat. No. 5,788,738by feeding ITO in forming gas (5% hydrogen-95% argon). The nanopowderswere dispersed in water and the UV-Vis absorption spectra were obtained.

It was observed that non-stoichiometry more than doubles the absorptionof infrared wavelengths. This experiment suggests that the change instoichiometry can be used to engineer and obtain unusual opticalproperties of a material.

Example 21 Electrical Devices

Titanium oxide nanopowders (white, 25 nm mean grain size) were heated inammonia for 12 hours at 600° C. The nanopowders converted to a deepblue-black color corresponding to non-stoichiometric nanopowder form (28nm mean grain size). The electrical conductivity of thenon-stoichiometric nanopowders was found to be more than ten orders ofmagnitude higher (resistivity of 1.5×10-2 ohm-cm) than the whitetitanium oxide nanopowders (greater than 108 ohm-cm, which iseffectively insulating). Electron microscopy on the blue-black powdersrevealed that the nanopowders were an oxynitride of titanium (TiON_(x)).It is also of interest to note that commercially availablemicrometer-sized TiN powders exhibit a resistivity of about 1.5 ohm-cm,about two orders of magnitude higher than the non-stoichiometricnanopowder. Thus non-stoichiometry offers unusual non-linear properties.This example suggests the utility of non-stoichiometry and nanostructureto engineer dramatic changes in electrical properties.

Example 22 Magnetic Products

Nanoscale ferrite powders can be heated in ammonia or hydrogen or boraneor methane to form non-stoichiometric ferrite. The powders can then betransformed into a form for incorporation into a device by techniquessuch as extrusion, tape casting, screen printing or any other methods orcombination thereof.

As an illustration, three toroids composed of a nickel zinc ferritematerial were sintered at 900° C. for 2 hours to obtain near-theoreticaldensities. Upon cooling, the toroids were wound with ten turns of 26gauge enamel-coated copper wire. Magnetic properties, includingimpedance, resistance, and serial inductance, were tested from 10 Hz to1 MHz with a Quadtech 7600 LCR meter and from I MHz to 1.8 GHz with aHewlett-Packard Model 4291A Analyzer. In each case, measurementconsisted of making a secure contact with the stripped ends of thewindings on the sample toroids and performing a frequency sweep. Oncetested, the three sample toroids were unwound and heated in a reducingatmosphere. Samples were ramped from room temperature to 800° C., heldfor one hour, then allowed to cool. During this cycle, a stream of 5%H-95%Ar flowed continuously over the samples. Upon recovery from thefurnace, a noticeable change in sample color was observed. Previously adark gray, the “reduced” ferrite toroids now had a lighter gray, mottledappearance. The reduced ferrite toroids were rewound with ten turns ofthe same wire and their magnetic properties were re-evaluated. Theobserved results indicated a surprising change in properties in thenon-stoichiometric samples: for a reference frequency of 1 MHz, theresistance increased by 732%, the inductance changed by 12.8%, and theimpedance reduced by 11.4%. That dramatic changes in resistance wereobserved and that the overall impedance of the devices remained largelyunaffected by the non-stoichiometry implies that non-stoichiometry leadsto a corresponding dramatic decrease in inductive reactance. In otherwords, non-stoichiometric ferrite cores exhibit higher magnetic loss.FIG. 2 shows an unusual change in resistance as a function of frequency,suggesting that the non-stoichiometry is changing the fundamentalperformance of the materials.

Yet another method of producing a magnetic device is as follows: 900 mgof manganese ferrite non-stoichiometric nanopowder and 800 mg of nickelzinc ferrite nanopowder are pressed at 90,000 psi in a quarter inch die.For all powders, 5 wt % Duramax® binder is added prior to pressing forimproved sinterability. Pellets composed of nanopowders are sintered at820° C. for 4 hours in a kiln with a 5° C./min ramping rate.Micrometer-sized reference pellets require sintering temperatures of1200° C. or more for 4 hours, everything else remaining the same. Aftersintering, all pellet diameters are 0.6 cm, and pellet heights are aboutI cm. Each pellet is wound with 20 turns of 36 gauge enamel coatedelectrical wire. The final wound pellets are wrapped with Teflon tape toensure that the windings stayed in place. These inductor samples can becharacterized with an Impedance/Gain-phase Analyzer. The performance canbe optimized by varying variables such as the aspect ratio, number ofturns, composition, and grain size.

Example 23 Resistors and Resistor Arrays

Resistors are a mature technology and have served various industries foralmost a century. They are produced in various forms and from varioussubstances. Wire wound resistors are one of the oldest technologies usedin the resistor market. The resistor is made by winding wire onto aceramic bobbin or former. The wire materials are often alloys, and thediameter and length of the wire determine the resistivity. Metal foilresistors are prepared from metal foil that sometimes is less than onemicrometer thick. The foil is stuck on a flat ceramic substrate and theresistance value engineered by precision etching a meandering pattern.These resistors are high value added and exhibit very low temperaturecoefficients of resistance. Film resistors are prepared by vapordeposition, anodization, or plating of metal or cermet or carbon film ona substrate, followed, if needed, by spiral cutting with a diamondwheel. Metal oxide resistors are prepared by depositing oxide vapor.Carbon film resistors are obtained by pyrolysis of hydrocarbon onceramic substrates. Once again, spiraling is commonly used to achievethe desired resistance value. Some resistors are prepared from coatingresistor inks consisting of a glass, metal particle dispersion in aviscous organic binder. The coating is stabilized by firing attemperatures around 600° C. The final resistance value is obtained byspiraling. These techniques are used for preparing discrete resistorchips, networks, or hybrid circuit systems. Desired resistance can befine tuned by air abrasion. Conducting plastic resistors are similar tometal film oxide resistors. They differ in the fact that organic binderis here replaced with a plastic and that the dispersant is often carbon.Sintered structure resistors are prepared by sintering SiC or CrO withsuitable dopants. These resistors are often used as thermistors, not asfixed linear resistors.

The presently claimed invention can be utilized in various embodimentsfor these devices. The composition of existing finished resistors can betransformed into non-stoichiometric forms a variety of techniques, suchas heat treating (400° to 2000° C.) the device in a reducing, oxidizing,nitriding, boronizing, carburizing, or halogenating atmosphere, or acombination of these, over a period of time ranging from a few secondsto hours, shorter times being preferred. Alternatively, existingprocesses to manufacture these devices may be suitably modified at anintermediate stage with one or more different processing steps to yielda non-stoichiometric form. Another embodiment of this invention is toproduce nanopowders of a non-stoichiometric substance and to thensubstitute the substance into existing processes and process it just asone would a stoichiometric substance.

For example, 65 m²/gm SiC_(0.8) nanopowders were produced and sonicatedin polyvinyl alcohol. The resulting dispersion was then screen printedon alumina substrate. After printing, the elements were fired atapproximately 300° C. for a half hour. The resistance of the resultingdevice was less than 1 megaohm. Addition of platinum and silver dopantsreduced the resistance further. Both p-type and n-type behavior wasobserved depending on the dopant.

Arrays are produced by printing multiple elements. The motivation forprinting arrays is to reduce the overall product size and to reduce thecost of placing multiple elements.

Example 24 Sensor Devices

Sensors are components which sense the component's environment orchanges in the component's environment. The environment may include astate of mass, energy, momentum, charge, radiation, field,electrochemistry, biological form, or a combination of one or more ofthese. This example discusses how the teachings in the presently claimedinvention can be utilized to design and practice better performingsensors, including chemical sensors. While the teachings here describe asingle layer thick film, they apply to thing film and multilayerarchitectures as well.

In a chemical sensor, each crystallite of the sensing material has anelectron-depleted surface layer (the so-called space charge layer)having a thickness “L” around it. This length is determined by the Debyelength and the chemisorbed species, and can be approximated by thefollowing expression: $L = {L_{D}\sqrt{\frac{2e\quad V_{s}}{kT}}}$where,

-   L_(D): intrinsic value of space charge thickness;-   eV_(s): height of Schottky barrier at grain boundaries (depends on    the sort and amount of adsorbates);-   k: Boltzmann

s constant; and

-   T: temperature.

If the crystallite size “D” is greater than twice the space charge layerthickness “L,” which is always true for sensors based on existingmicrometer-size grained stoichiometric materials, the electricalresistance of the sensor device is determined by the electron transportacross each grain boundary, not by the bulk resistance. The resistancein this regime can be expressed as:$R = {R_{o}{\exp\left( \frac{e\quad V_{s}}{kT} \right)}}$where R_(o): bulk resistance.

The generally accepted definition of device sensitivity of a device isgiven by (or is a simple variation of):$S = {\frac{R_{g}}{R_{a}} = {\frac{R_{o}{\exp\left( \frac{e\quad V_{sg}}{kt} \right)}}{R_{o}{\exp\left( \frac{e\quad V_{sa}}{kt} \right)}} = {\exp\frac{{e\_ V}_{s}}{kT}}}}$where,

-   R_(a): resistance of device in air; and-   R_(g): resistance of device in air containing an analyte.

Because “e_V_(S)” is independent of “D” until “D” is greater than twicethe space charge layer thickness “L,” it is no surprise that theobserved sensitivity of the sensor device is independent of crystallitesize in this regime. The above arguments lead to the natural question:what happens when D<2 L? In this nanoscale regime, the device resistanceis no longer just grain boundary controlled; instead, the bulkresistance of each grain becomes important. Since, “e_V_(S)” isdependent on the adsorbate type and amount, this change inphenomenological regime provides an unprecedented way to engineerextremely sensitive sensors. In effect, one can engineer the crystallitesize and the non-stoichiometry such that R_(g) becomes bulk graincontrolled (i.e., very high), while R_(a) remains grain boundarycontrolled (i.e., low). This changes “e_V_(S)” significantly, and sincethe sensitivity “S” depends exponentially on “e_V_(s),” this candramatically enhance the sensitivity of the sensor device. Enhancedsensitivity has been long sought in the sensor industry.

The benefits of nanostructured non-stoichiometric fillers may beexploited in monolithic or composite form. A composite, loosely defined,is a combination of two or more dissimilar materials, or phases,combined in such a way that each material maintains its individualcharacter. The properties of the composite depend greatly on thearrangement of the individual phases present. In completely homogeneouscomposites, the properties tend to be a combination of the properties ofthe distinct phases present, a combination that is often unobtainablewith metals, ceramics, or polymers alone. This makes composites uniqueand very appealing for applications which require a demanding andconflicting matrix of design needs. Sensors are one such applicationwhere conventional materials in monolithic form often excel in meetingsome design goals, but fail to meet others. Composites of nanoscalenon-stoichiometric substances can potentially provide the breakthroughwhere all the needs are simultaneously met. This embodiment isparticularly useful when the selectivity of the sensor needsimprovement.

Sensors (and sensor arrays) can prepared by numerous methods and thebenefits of nanoscale non-stoichiometric substances can be practicedwith any of these methods. In one embodiment, sensing films wereprepared by brushing on a slurry containing nanoscale non-stoichiometricpowders (and polymer, if appropriate) onto a screen-printed electrode ona substrate. The sensor electrodes were prepared using a Presco Model465 Semi-Automatic Screen Printer. This equipment facilitated automaticprinting, with the exception of loading and unloading the substrate. Thescreen used was from Utz Engineering, Inc. The screen was made fromstainless steel mesh and had a frame size of 8×10 inches, a mesh countof 400, a wire diameter of 0.0007 inches, a bias of 45 degrees, and apolymeric emulsion of 0.0002 inches. The gold electrodes were screenprinted on a 96% alumina substrate and then fired in air at 850° C. fora peak time of 12 minutes. Dopant polymers were dissolved in anappropriate solvent. Once the polymer was dissolved, non-stoichiometricnanopowders were added to the solution and sonicated for 20 minutes. Theslurry was then deposited onto an electrode using a small paint brush.Once deposited, the elements were allowed to dry in air at 100° C. for30 minutes to remove the solvent.

In an alternate embodiment, a screen printable paste was first prepared.The paste was again prepared from nanopowder and polymer. Thenanopowder, polymer, and catalyst (when included) were weighed out andmixed together in a mortar and pestle. Next, screen printing vehicle wasweighed out and transferred to the mortar and pestle where the twophases were mixed together. Finally, this paste was placed on a threeroll mill and milled for five minutes. The three roll mill allowed forhigh shear mixing to thoroughly mix the paste and to break upagglomerates in the starting nanopowder. After the paste was prepared itis screen printed on to the prepared electrodes, allowed to level, andthen dried at 100° C. This embodiment illustrates a method for preparingsingle elements and arrays of sensors.

Next, the sensing elements were screened, tested, and optimized forsensitivity, selectivity, and response time, as described below.

The sensitivity is calculated from the change in resistance of thesensor when exposed to a background and when exposed a vapor analytespecies in background and determines the threshold exposure levels. Asimple variation of the above equation describing sensitivity is:${Sensitivity} = \frac{R_{a} - R_{s}}{R_{s}}$where:

-   R_(a)=sensor resistance in background; and-   R_(s)=sensor resistance when exposed to analyte vapor.

The selectivity is a comparison of either the sensitivity of anindividual sensor to two different analytes or of two sensors to thesame analyte.${Selectivity} = \frac{{Sensitivity}_{a}}{{Sensitivity}_{b}}$

The response time is the time it takes for the sensor to detect a changein the surrounding environment, defined as the time required for thesensor to reach 90% of its peak resistance (R_(s)).

With non-stoichiometric nanoscale powders, low temperature sensingelements with sensitivity S greater than 1.5, selectivity greater than1.1, and response times less than 10 minutes can be obtained for widerange of gaseous and liquid analytes. With optimization, selectivitygreater than 2, sensitivity greater than 1.5, and response time lessthan 1 minute can be obtained at ambient conditions.

Some specific examples of analytes that can be sensed using theteachings herein, include, but are not limited to: carbon oxides (CO,CO₂), nitrogen oxides (NO_(x)), ammonia, hydrogen sulfide, borane,hydrogen, hydrazine, acidic vapors, alkaline vapors, ozone, oxygen,silane, silicon compounds, halogenated compounds, hydrocarbons, organiccompounds, metallorganic compounds, metal vapors, and volatileinorganics.

Example 25 Biomedical Products

Mechanical alloying can be used to prepare nanocrystallinenon-stoichiometric alloys. The feed powder Ti-4.9Ta-11 Nb-15.2Zr isloaded in non-stoichiometric proportions into a cylindrical hardenedsteel vial with hardened steel mill balls. The ball-to-powder ratio ispreferably high (5:1). The loading process is preferably done within anargon atmosphere glove box. The environment inside is maintained at anoxygen concentration of <100 PPM and moisture content of <3.0 PPM. Themill itself is set up outside of the glove box and the vial and millhousing cooled using forced air convection. After milling, the vial istransferred back to the glove box where the non-stoichiometric powder iscollected and submitted for analysis or further processing. To preparean orthopedic implant, the synthesized powders are uniaxially pressed.Poly(ethylene glycol) (PEG) may be used as a binder for compaction ofthe powders. PEG is added to the powders by preparing a 1 weight percentsolution in ethanol and wet mixing the solution with the alloyedpowders. The homogeneous mixture is air dried at room temperature. Apress can be used to compact the powders in a die. A uniaxial 11,250 lb.force is applied (resulting in 225,000 psi of pressure) which isappropriate for implant specimens.

One advantage of non-stoichiometric nanoscale powders is the potentialuse of non-toxic elements in orthopedic and other biomedical implants.In general, biomedical implants are engineered to control propertiessuch as strength, toughness, modulus, corrosion resistance,biocompatibility, porosity, surface roughness, and wear resistance. Thematerials described in the previous paragraph can be optimized to matchthe modulus of bone, a desirable characteristic of materials for somejoint replacement applications. In other embodiments, nanopowders can beutilized for drug delivery and as markers for diagnosis. Nanopowders canalso be utilized for enhancing the solubility of drugs in organic andinorganic solvents. In yet other embodiments, the teachings can beapplied to various products where inorganic and organic powders arecurrently being utilized, as known to those skilled in the art.

Example 26 Electronic Components

Electronic components, for example, disc and multilayer capacitors,inductors, resistors, filters, antennas, piezo devices, LED, sensors,connectors, varistors, thermistors, transformers, current converters,shields, or arrays of such components in conventional mount or surfacemount form, can be prepared using the teachings herein. As an example,to prepare varistors from nanoscale non-stoichiometric materials, apaste of the powders was prepared by mixing the powder and screenprinting vehicle with a glass stir rod. Exemplary compositions includeZnO_(1-x), Bi_(2/3)O, and other oxides. Silver-palladium was used as theconducting electrode material. A screen with a rectangular array patternwas used to print the paste on an alumina substrate. The processconsists of screen printing the electrode and rapidly drying the film ona heated plate. The process was attended and precautions taken toprevent electrically shorting the device. The final electrode wasapplied in the same manner as the first. The effectivenon-stoichiometric nanostructured-filler based composite area in thedevice due to the offset of the electrodes was small (0.2315 cm²).However, this offset may be increased or further decreased to suit theneeds of the application. The thick green films were co-fired at 900° C.for 60 minutes.

Such a device offers a means to control surge voltages. An accuratedetermination of device non-linearity, α, can be obtained using theempirical varistor power law equation:I=nV^(a)

where: I=current.

-   -   n=the varistor power coefficient.    -   V=voltage.

The value of a obtained for the nanostructured non-stoichiometric deviceis anticipated to be 10 fold higher than that achievable withmicrometer-sized stoichiometric fillers. It is also expected that theresistance of the boundaries would be lower, enabling clampingcapability of lower voltages and higher frequencies. Other componentsthat can specifically benefit from the high surface area ofnanostructured non-stoichiometric materials include but are not limitedto positive temperature coefficient resistors and barrier layercapacitors.

Example 27 Electrochemical Products

Electrochemical products, for example, batteries, electrolytic cells,corrosion inhibitors, electrodes in metallurgical applications and otherindustries, pH sensors, and electrochemical sensors, can benefit fromthe use of non-stoichiometric nanopowders. The most distinctive featureof these non-stoichiometric nanopowder materials is their uniquethermodynamic state and the large number of atoms situated in theinterfaces. A 10 nm nanocrystalline metal particle contains typically10²⁵ atoms which are situated on or near the interface per cubic meterof material; thus, 30% of total atoms in the material are situated inthe interfaces or on the surface and exhibit non-bulk properties. Such aunique ultra-fine structure of nanopowders, when applied toelectrochemical products, can lead to a drastic improvement of theirperformance. The ultra-fine (nanometer scale) microstructure ofnanostructured hydrogen storage materials, to illustrate, will not onlyenhance the thermodynamics and kinetics of hydriding and dehydridingprocesses, but also improve their structure stability, and thusreliability and life time.

Particularly, nanostructured materials offer the following motivationfor their utilization:

(i) Drastic Increase of Species Solubility or Capacity

The ultra-fine grain size of nanostructured materials gives an excessGibbs free energy to the system compared to the conventional largegrained (micrometer size) hydrides. This will significantly enhance thesolubility of solute atoms, including hydrogen, because:$\frac{C_{d}}{C_{\infty}} = {\frac{k\quad V}{RT}\frac{\sigma}{d}}$where:

-   C_(d) and C_(□)=solubilities of a solute in the material with    average grain size d and infinite grain size, respectively;-   R=gas constant;-   T=temperature;-   V=the molar volume of the solute;-   k=Boltzmann's constant;-   v=the surface energy of the grain.

Thus, theoretically, a 10 nm grained hydride is expected to have ahydrogen solubility 1000 times higher than a 10 μm grained hydride withthe same chemical composition. The use of non-stoichiometric nanoscalepowders offers to further enhance the thermodynamic and/or kineticpotential of the system. Other advantages of non-stoichiometricformulations, for example, faster and more economical processingconditions, still apply.

(ii) Significant Enhancement of Hydrogen Diffusivity

The large volume fraction of interface in nanostructured materials willresult in grain boundary diffusion dominating the overall diffusion inthe materials. The overall or effective diffusivity of solute atoms inthe material is given by:D ^(eff) =fD _(gb)+(1−f)D _(lt)where: D^(eff)=the effective or overall diffusion coefficient;

-   D_(gb)=the diffusion coefficient in grain boundaries;-   D_(It)=the diffusion coefficient within grains.-   f=the fraction of solute atoms on the grain boundaries.

Since D_(gb) normally is 10⁴ times higher than D_(lt), orD_(gb)>>D_(lt), and more than 30% of atoms are situated in the grainboundaries, the above equation can be rewritten asD_(eff)≈D_(gb)=0.3 D_(gb)<<D_(lt)

The solute diffusion coefficient in nanostructured materials, therefore,is expected to be 1000 to 10,000 times higher than in conventionalmicro-grained materials.

(iii) Reduction of Temperature and Pressure for Hydride Formation andDissociation

The excess free Gibbs energy due to the ultra-fine structure ofnanomaterials will also lead to significant change in phasetransformation temperatures such as the hydride formation temperature.The phase transformation temperature change _T due to the ultrafinestructure is related to the grain size d by:${\_ T} = {\frac{\left( {\sigma_{1} - \sigma_{2}} \right)T_{c}}{L}\frac{k}{d}}$where:

-   σ₁,σ₂=specific surface energies of phase 1 and phase 2,    respectively;-   L=the heat of transformation from phase 1 to phase 2;-   T_(c)=the phase transformation for the bulk material;-   k=Boltzmann's constant.

Thus, the phase transformation temperature is expected to change as thegrain size decreases. Because the hydrogen dissociation pressuredecreases as the dissociation temperature decreases, the ultra-finemicrostructure of nanostructured materials in general, andnon-stoichiometric nanomaterials in particular, is preferable designguideline to a lower hydrogen dissociation pressure. This is verydesirable in hydrogen storage technologies. This basic guideline forpractice applies even to other electrochemical couples and systems suchas batteries and electrodes. The benefits of lower phase transformationtemperature have utility beyond electrochemical products and apply tothermal (e.g. heat transfer fluids) and other applications as well.

(iv) Higher Resistance to Pulverization During Hydriding/DehydridingProcesses

High strength is essential to pulverization resistance due to largelattice expansion and contraction during hydriding/dehydridingprocesses. The ultrafine grain size of nanostructured hydrides offers adrastic improvement in their structure stability. This can be inferredfrom the yield strength of a material which is related to its grain sized by the Hall-Petch relationship:$\sigma_{y} = {\sigma_{o} + \frac{k_{y}}{\sqrt{d}}}$

Fracture toughness, K_(1C), is related to grain size by:K _(1C)=σ_(y) √{square root over (πa _(c) )}where:

-   σ_(y)=the yield strength;-   σ_(o)=the frictional stress needed to move the dislocation;-   k_(y)=a constant;-   a_(c)=the critical crack length.    This indicates that as the grain size decreases from 10 μm to 10 nm,    both the strength and fracture toughness are expected to increase by    a factor of 30, which in turn leads to a higher resistance to    pulverization. Thus, electrochemical products in particular, and    other products in general, can benefit from superior performance of    nanostructured materials.

Some specific examples for the use of non-stoichiometric nanomaterialsin electrochemical products would be rare-earth doped or undopedMg_(1.8)Ni, Ni—ZrNi_(1.6), La_(0.9)Ni₅, and other existing compositionswith non-stoichiometry as explained previously.

Example 28 Energy and Ion Conducting Devices

Stoichiometric nanoscale 9 mole % yttria-stabilized cubic zircorniapowders (Y₁₈Zr₉₁O₂₀₉) are first reduced at moderate temperatures (500°to 1200° C.) in a forming, or reactive, gas to yield non-stoichiometricY₁₈Zr₉₁O₁₈₅ nanopowders. These powders are pressed into 3 mm diameterdiscs and then sintered to high densities. The disks should bepreferably sintered at low temperatures (preferably 800 to 1200° C.) forshort times (preferably 6 to 24 hours) to minimize grain growth. Thesenanopowders, as discussed before, can be readily sintered to fulltheoretical densities (99% or more). Careful control and optimization ofthe sintering profile and time can reduce the sintering temperature andtime further. The two ends of the cylindrical discs so produced are thencoated with a cermet paste consisting of a mix of silver and nanoscalestoichiometric yttria stabilized zirconia powder (a 50-50 wt % mix).Non-stoichiometric nanoscale powders can be utilized in the electrode aswell. Platinum leads are then attached to the cermet layer. This devicecan serve as an oxygen-conducting electrolyte with significantly higheroxygen ion conductivity at lower temperatures than conventionalelectrolytes. Exemplary devices include but are not limited to oxygensensors, oxygen pumps, or fuel cells. In this example, the degree ofnon-stoichiometry is arbitrarily chosen, and further optimization can bebeneficial to the economics and performance.

The benefits of this invention can be utilized even when the yttria inthe zirconia formulation is replaced with other stabilizers such asscandium oxide, calcium oxide, and other oxides. Similarly, other GroupIV oxides (e.g. ceria) and perovskites can be used instead of zirconia.Other ion conductors, for example, beta alumina and NASICONs for sodiumion, lithium nitride and LISICONs for lithium ions, silver iodide forsilver ions, Rb₄Cu₁₆I₇Cl₁₃ for copper ions, polymers such as nafion andperovskites for hydrogen protons, can all benefit from the use ofnon-stoichiometry in the ion conducting electrolytes and/or electrodes.

Example 29 Dopants in Formulations and Inks

Often, it is necessary to add secondary phase particles to a primarypowder element to achieve a desired property, such as temperaturecoefficient of the dielectric constant. For example, commercialcapacitor formulations of the Electronic Industry of America (EIA) X7Rdesignation contain additions of dopants (e.g. tantalum oxide, niobiumoxide, nickel oxide, bismuth oxide, silicates, titanates, and manganeseoxide) which are added to the base barium titanate powder to tailor thetemperature-capacitance or other characteristics of the material. Thesecondary phase particle additions are also often used to facilitate lowtemperature sintering. These materials include, but are not limited to,bismuth oxide, copper oxide, titanium oxide, silicon oxide, and vanadiumoxide.

In these powder mixtures, it is usually desirable to achieve a uniformmixture of the primary phase particles and the secondary phaseparticles. This can be difficult if the volume fraction of the secondaryparticles is small and if the size of the secondary particles is largein relation to that of the primary particles. The problem is that thenumber fraction of the secondary particle phase is small in relation tothat of the primary particle phase; thus, the relative distances betweenthe secondary phase particles can be rather large. This can translate toa non-uniform distribution of the secondary phase particle speciesthroughout the powder element and also in the microstructure of thefinal product.

Nanocrystalline powders in general and non-stoichiometric powders inparticular produced by any technique can reduce the size of thesecondary particles relative to primary particles and in turn, increasethe number fraction of the secondary particles in the powder element.This will translate to a uniform mixedness in the powder element and inthe product's microstructure.

To illustrate, 80 nm (preferably 40 nm, more preferably 10 nm)Ta_(2/3)O_(0.9), Nb_(2/5)O_(0.74), NiO_(0.98), Mn_(1/2)O_(0.9),Bi_(2/3)O_(0.45), Cu_(1.9)O, TiO_(1.1), SiO_(1.55), and V_(2/5)O_(0.975)are examples of non-stoichiometric nanopowders that can be used asdopants in device formulations and inks.

Example 30 Chemical Sensors

This example is from U.S. patent application Ser. No. 09/153,418 whichwas incorporated in this specification and is herewith presented forconvenience.

An array was formed from the following components: (1) NanostructuredSnO₂ powder; (2) Nanostructured TiON powder; (3) Polyvinyl chloride(PVC); and (4) Polyaniline (PAN).

The SnO₂ nanopowders were prepared as follows: First, 25 g of SnCl₄≅5H₂Owas dissolved in 120 ml of deionized water and then 120 ml of denaturedalcohol was added to the solution. Next, a solution of 14% NH₄OH wasprepared from 28-30% NH₄OH and deionized water. Both solutions were thenplaced in a freezer at approximately −5° C. for 30 minutes. Thesolutions were then removed from the freezer and the SnCl₄ solution wasprecipitated, forming Sn(OH)₄, dropwise under constant stirring with theNH₄OH solution. As the solution thickened the stir rate was increasedand a glass rod was used to break up the gelatinous mixture. Theprecipitation was continued until the pH of the solution wasapproximately 9. The precipitate was then vacuum filtered in a 3 LBuchner funnel. It was washed several times with deionized water, thenseveral times with denatured alcohol to minimize agglomeration. Theprecipitate was then collected from the filter and dried at 100° C. fortwo hours and ground with a mortar and pestle to a fine powder. Thepowder was heated at 20 EC/minute to 450° C. and calcined for 30minutes, forming nanopowders of SnO₂. The TiON was prepared by reducingnanoscale titania (TiO₂) (Degussa TiO₂ as received) in an ammonia (NH₃)stream in a rotating furnace at 750° C. for 24 hours. Polymers used wereobtained from Sigma-Aldrich and used as received.

To prepare the sensors, electrodes were prepared on an alumina substrateby screen printing, using a semi-automatic screen printer. Thisequipment facilitates automatic printing, requiring manual interventiononly for loading and unloading the substrate. The screen used was fromUtz Engineering, Inc. The screen was made from stainless steel mesh andhas a frame size of 8×10 inches, mesh count of 400, wire diameter of0.0007 inches, bias of 45 degrees, and a polymeric emulsion of 0.0002inches.

Gold screen printing paste (Electro Sciences Laboratory, #8835-1B) wasused for the electrodes. They were printed on 10 mil thick, 96% aluminasubstrates laser scribed into ¼″×¼″ sections for easy separation(Laserage Technology Corporation). Once printed the electrodes wereallowed to level, dried at 100° C. for 10 minutes and finally fired at apeak temperature of 850° C. for 12 minutes. Then, 0.5 grams of SnO₂nanopowder was suspended in 2 ml of isopropanol by sonicating for 20minutes. The active sensing layer was then deposited by using a pipetteto place two drops of the slurry onto the electrode. This was thenallowed to dry at 100° C. and finally fired at 400° C.

To prepare the arrays, screen printable pastes were first prepared asfollows:

-   1. 98/2 (by weight) SnO₂/Polyaniline+catalyst

2.11 grams SnO2 nanopowder, 0.05 grams PAN, 0.04 grams Palladium acetate(Aldrich, 98%, 20,586-9) and 0.05 Dihydrogen hexachloroplatinate(Alfa-Aesar, 11051) were weighed out and mixed together in a mortar andpestle. Next, 1.1 grams of screen printing vehicle (Electro-SciencesLaboratories, #400) was weighed out and transferred to the mortar andpestle where the two phases were mixed together. Finally, this paste wasplaced on a three roll mill and milled for five minutes. The three rollmill allowed for high shear mixing to thoroughly mix the paste and tobreak up agglomerates in the starting nanopowder.

-   2. 98/2 (by weight) SnO₂/Poly(vinyl chloride)+catalyst

0.03 grams of Palladium powder (Aldrich, submicron, 32,666-6) was addedto 2.37 grams of a paste prepared as above, substituting poly(vinylchloride) for PAN. The paste was placed on a three roll mill and milledfor five minutes.

-   3. 98/2 (by weight) TiON/Polyaniline+catalyst

3.00 grams TiON nanopowder, 0.06 grams PAN, 0.11 grams Palladium acetate(Aldrich, 98%, 20,586-9) were weighed out and mixed together in a mortarand pestle. Next, 1.5 grams of screen printing vehicle (Electro-SciencesLaboratories, #400) was weighed out and transferred to the mortar andpestle where the two phases were mixed together. Finally, this paste wasplaced on a three roll mill and milled for five minutes. The three rollmill allowed for high shear mixing to thoroughly mix the paste and tobreak up agglomerates in the starting nanopowder. After the paste wasprepared it was screen printed onto the prepared electrodes, using aPresco Model 465 Semi-Automatic Screen Printer, allowed to level andthen dried at 100° C. The sensors were then thermally treated, at 250°C., to activate the Palladium acetate to PdO.

The pastes prepared were screen printed, one at a time, onto threeadjacent electrodes using a Semi-Automatic Screen Printer. The fourthelement was baseline and blank. The active printed elements were allowedto level, dried at 100° C. for 10 minutes and finally thermally treatedat 250° C.

For testing of the arrays the sensors' resistance were allowed tostabilize in a background of 200 ml/min of air at room temperature. Thetest was begun and background data was taken for 1 minute. Then, the 200ml/min air flow was switched to flow through a bubbler containing eitherSigma Pseudo Explosive Scent, nitrotoluene or cyclohexane. Air passingthrough the bubbler picked up analyte vapor and then passed into thetesting unit. Data was collected for 3 minutes. Finally, the flow wasreturned to 200 ml/min of plain air and data were collected for 2minutes.

The resistance of the array was measured simultaneously in parallelusing a resistance meter and a printed circuit board. The testing unitallowed the determination of composite resistance and individualresistances as different gases were passed over the array.

It was found that the SnO₂/PVC+Pd catalyst could sense nitrotoluenevapors; the other formulations had no response to nitrotoluene vapors.SnO₂/PVC+Pd catalyst and SnO₂/PAN+catalyst responded to Sigma PseudoExplosive Scent; TiON/PAN+Pd catalyst has no response to Sigma PseudoExplosive Scent. All three compositions were sensitive to cyclohexane.

Example 31 Electroceramics

This example is from U.S. patent application Ser. No. 09/153,418 whichwas incorporated in this specification and is herewith presented forconvenience.

Electroceramics are important components of numerous products forelectrical, communication, electronic, and sensor/actuator industries.Illustrative examples include capacitors, inductors, resistors,insulators, antennae, interference filters, MMIC, transducers,transformers, electromagnets, piezo devices, packaging, batteries, anddisplays. Significant improvements in existing electroceramics or novelformulations of electroceramics can make significant impact on a widerange of products.

It is well established in electroceramic device industry that pure,single or two metal oxides rarely offer a property envelope that meetsall the needs of real life applications. It is necessary to add dopants,substituents, and additives to stabilize the performance and reliabilityof the device over variations in temperature, variations in voltage,variations in frequency, and manufacturing and other process conditions.For example, in capacitors, the following additives are routinely added:CaTiO₃, SrTiO₃, TiO₂, ZrO₂, rare earth oxides, (e.g., as donor dopants,sintering aids, and Curie point shifters). Additions of additional metalions can also have a profound effect on the dielectric constant of thematerial as evidenced by Table 4. TABLE 4 Dielectric Constants as aFunction of Material Chemistry Density EIA rating Dielectric ConstantBaTiO₃ content (wt %) (g/cm³) NPO 75 10-50 4.20 BX, X7R 3000 90-98 5.80Z5U 8000 84-94 5.80 Z5V 18000 80-94 5.80

It is common in practice to discover satisfactory electroceramicformulations by a trial-and-error approach. The cost of developing suchformulations is high and thus, novel applications and novel, highperformance, reliable electroceramic devices are slow and expensive todevelop and manufacture. This invention addresses this limitationthrough the use of combinatorial screening.

For electroceramics screening, an electrode (Ag/Pd) array of 625 (15×15)elements is printed. Next, BaTiO₃, SrTiO₃, TiO₂, WO₃, NdO, Fe₂O₃, andMnO₂ films are printed using a piezo-array inkjet printer controlled bya PC. The array synthesized is a Taguchi Statistical Set derived fromseven oxides and eight concentration levels (2%, 8%, 20%, 40%, 60%, 80%,92%, 98%). This is followed by printing the second layer of theelectrode. The electrode ends are terminated. The array is then be curedand sintered to 1150° C. at a 10° C./min ramp rate. This ensures theremoval of organics, microstructural integrity, solid state synthesisreaction completion, and defect elimination in the layers of eachelement.

The performance of each element is determined in rows and columns formatby measuring the capacitance and temperature coefficient of capacitance(TCC) using a cap bridge; impedance response as a function of frequencyis measured using a Hewlett Packard impedance analyzer (HP4191A). Theloss factor is determined. A row and column format testing is chosen toreduce the time to parallel test the elements. Each element could bescreened one element at a time instead, but that would be time consumingand expensive. By vector searching the array, promising vectors of thearray can be discovered first and these can then be related to crossvectorial analysis to identify the candidate elements that have highperformance in both a row and a column. Note that, since each vectorconsists of capacitors in parallel, the capacitance of each vector j canbe modeled as: $C_{j} = \frac{1}{\frac{1}{\sum\limits_{i}\quad C_{ij}}}$where C_(ij) is the capacitance of array element ij. If row i and columnj both offer promising characteristics, element ij is an expectedcandidate for further specific screening and testing. A heating pad anda thermistor layer embedded underneath each capacitor element can beused to maintain and monitor the temperature. This assembly can assistthe determination of elements' TCC. The voltage coefficient ofcapacitance and dissipation factor can also measured.

The breakdown strength of the components is determined by increasing theapplied voltage until a direct short occurs. This breakdown inirreversible and determines the absolute maximum voltage at which thedevice can be used. A Hipotronics HD 100 series HIPOT tester can usedfor this purpose, for example. To eliminate the possibility of arcingacross the part at high voltages, it is preferred that the part beimmersed in dielectric fluid before the voltage is applied. Destructivetests such as this, of course, should be done after nondestructivetesting is complete.

Example 32 Optical Switches

This example is from U.S. patent application Ser. No. 09/153,418 whichwas incorporated in this specification and is herewith presented forconvenience.

In many substances, changes in chemical composition, pressure ortemperature can induce metal-to-insulator transitions. Although dramaticchanges in optical and electrical properties accompany such transitions,their interpretation is often complicated by attendant changes incrystallographic structure. Yttrium, lanthanum and the trivalentrare-earth elements form hydrides that also exhibit optical propertytransition. A shiny mirror-like thin film of yttrium or lanthanum with alayer of palladium through which hydrogen can diffuse can turntransparent when it absorbs hydrogen. But, once the Y or La thin filmhas been hydrogenated, it does not decompose readily. Thus, thetransparent metal hydride film can not easily be turned back to theopaque state by dehydrogenation. For this reason, the interestingoptical properties of Y and La metal hydrides have not found immediateapplication. However, a number of binary and ternary reversible hydrogenstorage alloys have been studied and developed in past two decades. Byadopting combinatorial approach, a large group of metal hydrides can besynthesized and their optical properties investigated in a relativelyshort period.

In these embodiments of the invention, optical switchable thin films aresynthesized in a sputtering system, for example one that offersdeposition, etching and plasma processing capability. Optical quartzplates with about 0.5-1.0 mm thickness are used as the substrates. Astainless steel foil is used to fabricate the physical masks. Thelibraries are generated by overlaying a primary physical mask,containing a grid of 16 openings (or any desired number), with a seriesof secondary masks. The thickness of each member may vary depend on theindividual composition. A 20 nm Pd cap layer is coated on all librarymembers homogeneously. The remaining area on the substrate, which mustreflect light completely, is coated by gold deposition with thirdblanket mask. A 16-member binary library derived from Ni, La, Ce, Y andZr is synthesized; in this example, each site is 2 mm by 2 mm in size,but this can reduced if desired.

The composition of individual binary alloy films is determined by thethickness of each component deposition layer. For example, a 100 nm Lafilm overlapping a 100 nm Ni film is expected to produce the binaryalloy LaNi after sintering. The library is then sintered to ensure theformation of the desired binary alloys by solid state reaction. XRD canbe used to verify the crystal structure and phase composition. Thethickness of films is measured by SEM.

The combinatorial library of optical switch materials is theninvestigated to determine how their optical properties are influenced byhydrogen. In this example, the experimental investigation focuses onoptical switch capability and, in particular, on reversibility.

To verify the optical switch capability of the different alloy films,the thin film array (library) is placed in a dark chamber that can beevacuated by a vacuum pump and filled with hydrogen at a desiredpressure. A visible light beam is introduced that hits the thin filmarray through the optical window of the dark chamber. A photodetector(digital camera) monitors the back side of the array. When hydrogen isintroduced into the dark chamber gradually, the alloys in the arrayreact with it to form different metal hydrides with differingtransparencies. The photodetector captures the light transmitted throughthe metal hydride films and convert the signals into digital data.Analyzing the data collected, the optical switch capability of eachindividual alloy is assessed. The optimal composition of alloy is onethat offers largest optical switch capability at moderate hydrogenpressure.

The reversibility of optical switching, e.g., two direction switching,is an important optical property for some potential applications, suchas hydrogen sensors and radiation shield devices. To determine oroptimize a material for such a device, after hydrogenation, the hydrogenis evacuated from the dark chamber by a vacuum pump. The metal hydridesin the library decompose to release hydrogen (an embedded heaterunderneath each element can be used to assist the decomposition, or thetest apparatus can be placed inside a furnace). The transparency of thefilms decreases during the de-hydrogenation process. The photodetectorobserves and records the decrease in the film transparency. Thisdecrease is expected vary for each film, because of the differentthermodynamic stabilities of the individual library members.

Example 33 Catalysts

This example is from U.S. patent application Ser. No. 09/153,418 whichwas incorporated in this specification and is herewith presented forconvenience.

This example illustrates the use of this invention for discovery ofcatalysts. Alternative catalytic materials have the potential to exertan enormous impact on the chemical and energy industries. Theseindustries are two of the largest in the U.S., with individual salesexceeding several hundred billion dollars. About 90% of chemical andenergy processes and over 20% of U.S. industrial products in generalinvolve catalysis.

Breakthroughs in catalytic materials can lower operating costsassociated with energy, raw materials and environmental improvement;reduce capital costs for investment in new processing technologies;accelerate discovery of competitive and environmentally superior processchemistries; enable novel products and technologies; and reducedependence on precious metals for catalytic applications. Clearly, thesignificance of innovation in catalytic materials is high. Combinatorialscreening offers an opportunity to rapidly develop new catalyticmaterials.

In this embodiment of the invention, first a microfabricated reactorarray is formed. (The described procedure may also be performed using amacro-array of reactors). This structure features a parallel array ofreactors each of which is identical to other elements in the array. Thedimensions of the array are designed to reduce pressure drop, ensureflow uniformity in each reactor, prevent short circuiting, enabletemperature control, and provide for an architecture that favors theanalysis of reaction being studied and the reliability of the analysis.

One method is to build the reactor from silicon micromachining; that is,by first forming an array of reactor cavities (pits) that can hold knownand desired quantity of catalyst candidates. The cavities are connectedto the product side surface with holes. Each pit is filled with ananostructured or other high surface area form of a candidate materialand covered with a mating part micromachined to ensure isolation of eachreactor cavity and provided with holes to connect the cavity to the feedside. The silicon micromachining technique can also be used to addheaters underneath or around each reactor cavity and provide forsensors, optics, or microelectronics for analysis of the reaction.

The silicon micromachining technique is limited by the materiallimitations of silicon. Many side reactions can occur at hightemperatures and refractory reactor arrays are desirable in theseapplications. Anodized alumina is an excellent candidate for buildingsuch microfabricated reactor arrays. Anodized alumina naturally formsaligned pores that can be utilized for carrying feed into the reactorcavity and to carry products out of the reactor cavity, as more fullydescribed in commonly assigned U.S. application Ser. No. 09/103,203,incorporated herein by reference. Other self-assembled or desktopmanufactured or mold manufactured refractory ceramics can be utilized toform such reactor cavity arrays as well. Micromachined arrays of onematerial can also be used as imprints and molds to form reactor arraysfrom other materials.

In each case, the number of array elements is kept greater than 1, morepreferably greater than 100, even more preferably greater than 10,000,and most preferably greater than 1,000,000. The array so prepared has ineach cavity a nanopowder or another high specific surface area form of apotential catalyst material. If the objective is catalyst discovery, thecavities are filled with an array of different candidate materialformulations, e.g., doped or undoped, inorganic or organic, homogeneousor heterogeneous, porous or non-porous, and stoichiometric ornon-stoichiometric. The array elements can be arranged in symmetry orstacked. Reactor cavities may be arranged in series and may be ofvarious shapes and sizes. Valves and control structures may bemicromachined or otherwise added to assist control of individual reactorcavity. If the objective is optimization of a catalyst material, then arow or column of cavities may show a gradient in composition as desired,where the gradient is incremental or arranged according to statisticalpattern such as Taguchi search and others that are known to thoseskilled in the art.

The testing for catalytic activity is done using parallel screeningsearch technique such as the bisectional search, the golden mean search,or the Fibonacci search. To illustrate without limiting the scope, thisexample discusses the bisectional search for the discovery of a catalystfor a gas phase reaction for which no catalyst is known. To begin, halfof the array is isolated and completely covered to prevent anyinteraction with feed gases. The collective response of the catalystcandidates in the other half is collected by flowing the feed gasthrough and collecting the product gas. The product gas is analyzed. Ifthe product gases show no signature of the desired species, it isconcluded that the candidate catalysts in tested half do not have anypotential candidate catalyst that is desired. Any catalysts within thecandidate set must be present in the untested half.

On the other hand, if a desired product species is detected in thetested half, then it is concluded that one or more of the candidateformulations in that half have the desired catalytic activity. In thissituation, half of the tested half (one quarter of the array) is furthercovered and isolated and the remaining quarter tested. If the test showsthat the tested quarter has no signature of the desired species, it isconcluded that the candidate catalysts in tested quarter does not haveany potential candidate catalyst that is desired. It is furthermoreconcluded that the active catalyst must be in the other quarter giventhe fact that the previous test had indicated that at least oneformulation is catalytically active. It is to be noted that a positivetest in one section does not necessarily mean that the other section isunpromising and negative. The objective and correct conclusion that canbe drawn with certainty is the confirmed absence of activity. In eachstep, the search is bisectionally focused on smaller and smallersections that give positive results, while the sections that givenegative results are eliminated. Such a bisectional search quickly canhelp eliminate unpromising candidates.

The isolation technique in parallel search techniques can be an externalmask or an embedded or attached valve that is electromagnetically,mechanically, magnetically, thermally, or otherwise switched into on andoff positions. A preferred search technique is the golden mean search.The mask can be simple or complex patterned. An example of simplepattern is closed arc or a rectangle. An example of complex pattern ishole filled arc or hole filled rectangle. The preferred pattern issimple.

In case of optimization of catalytic materials, a similar search methodmay be used. However, then each section must be searched and thedecision to focus should be based on relative performance of eachsection. Better performing sections should be naturally selected overmore poorly performing sections. Sections that fail to perform should beeliminated from the selection process. Sections that fail to perform maybe reused as starting materials, by reformulating, doping, heating,reacting and/or otherwise modifying the array, and then retesting foractivity.

With automated valves, a control unit may be integrated in the searchprocess. In such architecture, sections of feed valves may be closed andthe product gases analyzed on-line or in batches, the preferred methodbeing on-line. When undesired changes in product composition(selectivity and yield) are detected as a section is brought on-line,feed valves in the said section are closed or left open one by oneautomatically. A valve is left open if the change in product compositionis desired, and the valve is closed if the change in product compositionis undesired or indifferent. Such natural selection of populations canhelp eliminate weaker candidates and identify stronger candidates tomeet the search and optimization objectives.

The benefit of using mathematical search algorithm such as the goldenmean search is that the number of actual tests needed is reduced by morethan half, often less than a square root of the actual number ofcandidates. Thus, if the library consists of 10,000 elements, routineone-by-one search would require 10,000 tests, while the searchalgorithms disclosed will typically require about less than 5,000 testsand often about 100 tests. In case of a library of 1,000,000 elements,the search algorithms disclosed will often require about 1,000 tests.

The technique disclosed can be used even when the actual testing ofproduct may not be simple. In such cases, secondary products or effectsmay be tested. For example, the temperature of the catalyst, theradiation from catalyst, the concentration of a byproduct (e.g.,hydrogen, water, carbon dioxide, ammonia, carbon monoxide, nitrogen, orother species), the pressure of the reaction gases, the flow rate fromthe reactor cavity, the electrochemical activity, or the nuclearradiation from the reaction may be monitored. The search methodsdescribed above can be applied to these measurements as well as todirect measurements of the desired product species. When sensors fordirect monitoring of desired products or direct monitoring of byproductsor effects are available and can be embedded, attached, or functionallypositioned in or near the micromachined reactor, the search may becompleted instantly by monitoring the sensor response as the feed flowsthrough the reactor array.

The catalyst screening method may be applied to search of catalysts forliquid phase reactions, homogeneous reactions, solid phase reactions,biochemical reactions, or complex reactions. This technique can be usedfor searching and discovering and optimizing biocatalysts orpharmaceuticals or molecules with bioactivity.

Example 34 Resistors

This example is from U.S. patent application Ser. No. 09/153,418 whichwas incorporated in this specification and is herewith presented forconvenience.

Resistors that do not vary with changes in environment are used innumerous electrical and electronic products. Resistors that do vary withchanges in its environment are used in sensing applications.Illustrative, but not limiting, examples of sensing applications includeresistors whose resistance changes with radiation exposure(photoconductors, photodetectors, bolometers, and radiation sensors),electrical field (electromagnetic sensors), magnetic field (data storageread heads), chemicals (chemiresistive sensors), pressure(piezoresistive sensors), and heat flow (thermistors). This exampleillustrates how this invention can be applied to both types ofresistors.

Two sets of inks were prepared for the studies. One set consisted ofmetal nanopowder doped resistive inks and the second of ceramicnanopowder doped resistive inks. In each of the preparations, the inkand a selected amount of additive were weighed out and mixed togetherwith a mortar and pestle. Table 5 shows the composition of the inks.TABLE 5 Compositions of Inks for Combinatorial Studies Set 1 Set 2Resistive Ink ESL 3910 Resistive Ink ESL 3910 20 wt % Antimony doped ESL3910 5 wt % Al₂O₃ doped ESL 3910 20 wt % Palladium doped ESL 3910 10 wt% Al₂O₃ doped ESL 3910 20 wt % 95/5 Silver/Palladium 15 wt % Al₂O₃ dopedESL 3910 doped ESL 3910

Six arrays of each set of inks were screen printed on to a previouslyprinted Silver/Platinum electrode. All screen printing was accomplishedusing a semi-automatic screen printer.

The prepared inks were printed over each electrode one composition at atime. The printed material was dried at 100° C. between the printing ofeach composition. Once the array was completely printed and dried it wasfired at 850° C. for 10 minutes.

To test the arrays a Fluke multi-meter was utilized and the resistanceof each element was recorded. Tables 6 and 7 give the results of thearrays based on the resistive ink. TABLE 6 4/29 Combinatorial Studies,Set 1. Results are given in Ohms. Material 1 2 3 4 5 6 Ave. ESL 3910 1.41.3 1.3 1.3 1.3 1.4 1.33 Antimony doped ESL 3910 6.5 5.5 6.0 10.3 10.38.2 7.80 Palladium doped ESL 3910 1.5 1.4 1.4 1.5 1.5 1.4 1.45 Ag/Pddoped ESL 3910 1.0 1.0 1.0 1.0 1.0 1.0 1.00

TABLE 7 Combinatorial Studies, Set 2. Results are given in Ohms.Material 1 2 3 4 5 6 Ave. ESL 3910 1.3 1.2 1.2 1.2 1.3 1.1 1.22 5% Al₂O₃doped ESL 3910 1.3 1.3 1.2 1.2 1.2 1.2 1.24 10% Al₂O₃ doped ESL 3910 1.81.3 1.3 1.2 1.3 1.3 1.37 15% Al₂O₃ doped ESL 3910 1.8 1.8 2.1 1.5 1.81.8 1.80

The parallel testing of Set 1 (Table 6) indicated that adding metalpowder to the resistive ink can be used to tailor the resistance offormulation. The screening led to the discovery that antimony had anabnormally large effect, increasing the resistance approximately fivetimes more than the other tested materials. The screening also indicatedthat the addition of silver decreases the resistance 25%. The additionof palladium produced a minor change in resistance. Thus, in anyapplication where resistance of ink is to raised, the screeningdiscovered that antimony is the preferred choice. In any applicationwhere resistance of ink is to lowered, silver is the preferred choice;

The parallel testing of Set 2 (Table 7) indicates that adding aluminapowder to the resistive ink can also tailor the resistance of the ink.The screening led to the identification that alumina nanopowders havestatistically insignificant effect on the resistance of the ink atlevels below 5%. The addition of ceramic powder above 5% can be used tooptimize the resistance of the resistive ink.

Example 35 Thermoelectric Materials

This example is from U.S. patent application Ser. No. 09/153,418 whichwas incorporated in this specification and is herewith presented forconvenience.

Thermoelectric devices convert thermal energy into electrical energy orelectrical energy into thermal energy. Inherent advantages of thesedevices include portability, reliability, simplicity, flexibility,quietness, and environmental benignity. High-performance thermoelectricmaterials can enable the manufacture of thermoelectric refrigeratingdevices with efficiencies above those achievable with chlorofluorocarbonbased compressors. This can help launch the production of all solidstate, high reliability, low power, low vibration crycoolers foradvanced electronics and detectors, as well as refrigerator units withno pressure vessel, moving parts, or acoustic signature. In addition,such materials may also be used for thermoelectric power generation fromeither a fuel based heat source or for exhaust heat recovery. Thebiggest obstacle for thermoelectric devices to be widely used is the lowefficiency of thermal/electrical energy conversion limited bythermoelectric materials with which these devices are made. The key tosuccessful commercialization of thermoelectric devices, therefore, to alarge degree, depends on the development of high-performancethermoelectric materials.

The performance of the thermoelectric material is generally evaluatedthrough its so-called the figure-of-merit, which is defined as$Z = \frac{\alpha^{2}\sigma}{\lambda}$where α is the Seebeck coefficient, λ the thermal conductivity, and σthe electric conductivity of the material. The dimensionlessfigure-of-merit ZT is commonly used. A high-performance thermoelectricmaterial should have a low thermal conductivity to prevent a significantportion of the heat from flowing down the temperature gradient, a highelectric conductivity to reduce the energy loss due to the Jouleheating, and a high Seebeck coefficient to have high efficiency ofthermal/electric energy conversion. That is, it should have a very highZT.

Efforts to develop high-performance or high ZT thermoelectric materialsdate back many years. Many material systems have been explored one at atime, with a focus on increasing the electrical conductivity anddecreasing thermal conductivity. However, the nature of these materialsand correlation of thermal and electrical conductivity place limits onpossible improvement of the figure-of-merit of the traditionalthermoelectric materials. All the currently-available thermoelectricmaterials have figures-of-merit less than or equal to 1 for both roomtemperature and cryogenic applications.

Examples compositions include bismuth telluride, bismuth selenide,bismuth antimonide, quasicrystalline alloys, skutterudites, and complexformulations of various chalcogenides and alloys. There is a need forformulations that show ZT higher than 1.0, preferably higher than 2.0,and even more preferably higher than 3.0, and most preferably withCoefficient of Performance that would make solid state devicesfunctioning close to Carnot efficiencies.

The emergence of nanostructured materials, however, opens up a newchapter in designing and synthesizing advanced materials. When thedimension of the material is reduced to 2-, 1-or even 0-dimensions, theclassic physical laws based on Newtonian physics, which govern thematerial's behavior, have to be replaced by those based on quantummechanics. Thus, nanostructured materials offer many novel propertieswhich can not be matched by traditionally-formed materials. Thisrecently emerging technology offers drastic improvement in materialsperformance-such as in thermoelectric applications, as described incopending and commonly assigned U.S. application Ser. No. 09/103,203,incorporated herein by reference. Combinatorial screening can be used todiscover and optimize nanostructured thermoelectric compositions inparticular and novel compositions in general.

Nanomaterials are ideally suited for the search of novel thermoelectricformulations because nanomaterials are a group of materials which havemany unique properties, including thermoelectric properties, unmatchedby traditional materials. The unique nano-confined microstructure offersthe following unique features:

1. Much lower thermal conductivity. In a nanostructured material, eachgrain is so small that the mean free path of phonons is solely limitedby the grain size. Thus, the thermal conductivity is proportional to thegrain size. A nanostructured material with average grain size of 10 nmwould have a thermal conductivity 100 times as low as that of thematerial in traditional form (with a grain size of ˜1000 nm);

2. Greater Seebeck coefficient. Nano-size particles, with diameter of˜10 nm, are quasi-0-dimensional materials. The quantum confinement willbe dominant in determining its thermoelectric properties. It isanticipated that in nanometer range, the Seebeck coefficient should bemuch greater than that of the micron-scale material.

3. Higher electrical conductivity. The large number of grain boundariesreduces the barrier for electrons to across into the neighboring grain,so that the overall electrical conductivity of the proposednanostructured thermoelectric material may not be lowered by grainboundary scattering of electrons within each grains.

4. Figure-of-merit ZT>>1. The lower thermal conductivity, higher Seebeckcoefficient and higher electrical conductivity of the proposedthermoelectric material will yield a much higher figure-of-merit. For amaterial which has a figure-of-merit close to 1 in its micron-scaleform, the proposed design of the material is expected to have afigure-of-merit much greater than 1.

5. Superior mechanical performance. The ultra-fine microstructure ofnanostructured materials leads to high mechanical strength, superiorplasticity and excellent toughness. The superior mechanical performancewill make nanostructured thermoelectric materials stronger, morereliable, and more economical in fabrication and post-processing (suchas machining).

6. Low processing cost. Nanomaterials can be densified at much lowertemperatures and much shorter cycle times than materials in thetraditional form, because of their high specific surface area, resultingin reduction of recrystallization temperature, enhanced diffusivity andthus sinterability.

7. Integrability with Existing Technology. Micron-scale powders arecurrently used by the industry to make thermoelectric devices. Theinvention uses nanostructured powders—an approach that enables facileintegration of the proposed technology into existing thermoelectricdevice technology.

One method that can be used for combinatorial screening is to begin bypreparing a library of combinatorial formulations, preferably innanostructured form. The resistance of the library can be measured by atechnique such as that described in Example 34, and the thermalconductivity of the formulation through the thickness would be measuredusing radiative techniques. For example, an array of radiation (infraredor suitable wavelength) sensors could monitor surface radiation.Alternatively, thermistors may be embedded underneath the thermoelectricfilm to sense the temperature gradient over each element while the otherface of the films is exposed to uniform temperature. It is important tomeasure the electrical and thermal resistance simultaneously to screenand optimize the thermoelectric formulation. The analysis may also bedone with a probe array structure used in combination with scanningmicroscopes and software to drive the probe array and interpret theresults thereof.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

1. A method of discovering ceramic nanomaterial for an applicationcomprising: forming an electroded film array comprising a plurality ofelements wherein each element of the electroded film array comprises aceramic nanomaterial film; determining a property of each element of theelectroded film array; and determining whether one or more of theplurality of array elements exhibit a property that is suitable for theapplication.
 2. The method of claim 1 wherein the ceramic nanomaterialcomprises non-stoichiometric nanomaterials.
 3. The method of claim 1wherein the ceramic nanomaterial comprises stoichiometric nanomaterials.4. The method of claim 1 wherein the first layer of electrode comprisesilver or palladium.
 5. The method of claim 1 wherein the array is aTaguchi statistical set.
 6. The method of claim 1 wherein the ceramicnanomaterial comprises one or more elements from the group consistingof—barium, titanium, strontium, tungsten, neodymium, iron and manganese.7. The method of claim 1 wherein the property comprises an electricalproperty.
 8. The method of claim 1 wherein the application comprises anelectroceramic application.
 9. A nanostructured product comprising theceramic nanomaterial discovered by the method of claim
 1. 10. The methodof claim 1 wherein the act of forming an electroded array comprisesprinting a first ceramic nanomaterial film on a first element and asecond ceramic nanomaterial film on a second element.
 11. The method ofclaim 10 wherein the first ceramic nanomaterial film comprises acomposition that is different from a composition of the second ceramicnanomaterial film.
 12. the method of claim 10 wherein the first ceramicnanomaterial film comprises a different concentration as applied thanthe second ceramic nanomaterial film.
 13. The method of claim 1 whereineach element comprises a ceramic nanomaterial film with a uniquecomposition as compared to each other element.